Date: 2026-03-31T05:46:26+00:00

Actual source code: snes.c

      1: #include <petsc/private/snesimpl.h>
      2: #include <petsc/private/linesearchimpl.h>
      3: #include <petscdmshell.h>
      4: #include <petscdraw.h>
      5: #include <petscds.h>
      6: #include <petscdmadaptor.h>
      7: #include <petscconvest.h>

      9: PetscBool         SNESRegisterAllCalled = PETSC_FALSE;
     10: PetscFunctionList SNESList              = NULL;

     12: /* Logging support */
     13: PetscClassId  SNES_CLASSID, DMSNES_CLASSID;
     14: PetscLogEvent SNES_Solve, SNES_SetUp, SNES_FunctionEval, SNES_JacobianEval, SNES_NGSEval, SNES_NGSFuncEval, SNES_NewtonALEval, SNES_NPCSolve, SNES_ObjectiveEval;

     16: /*@
     17:   SNESSetErrorIfNotConverged - Causes `SNESSolve()` to generate an error immediately if the solver has not converged.

     19:   Logically Collective

     21:   Input Parameters:
     22: + snes - iterative context obtained from `SNESCreate()`
     23: - flg  - `PETSC_TRUE` indicates you want the error generated

     25:   Options Database Key:
     26: . -snes_error_if_not_converged (true|false) - cause an immediate error condition and stop the program if the solver does not converge

     28:   Level: intermediate

     30:   Note:
     31:   Normally PETSc continues if a solver fails to converge, you can call `SNESGetConvergedReason()` after a `SNESSolve()`
     32:   to determine if it has converged. Otherwise the solution may be inaccurate or wrong

     34: .seealso: [](ch_snes), `SNES`, `SNESGetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     35: @*/
     36: PetscErrorCode SNESSetErrorIfNotConverged(SNES snes, PetscBool flg)
     37: {
     38:   PetscFunctionBegin;
     41:   snes->errorifnotconverged = flg;
     42:   PetscFunctionReturn(PETSC_SUCCESS);
     43: }

     45: /*@
     46:   SNESGetErrorIfNotConverged - Indicates if `SNESSolve()` will generate an error if the solver does not converge?

     48:   Not Collective

     50:   Input Parameter:
     51: . snes - iterative context obtained from `SNESCreate()`

     53:   Output Parameter:
     54: . flag - `PETSC_TRUE` if it will generate an error, else `PETSC_FALSE`

     56:   Level: intermediate

     58: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetErrorIfNotConverged()`, `KSPGetErrorIfNotConverged()`, `KSPSetErrorIfNotConverged()`
     59: @*/
     60: PetscErrorCode SNESGetErrorIfNotConverged(SNES snes, PetscBool *flag)
     61: {
     62:   PetscFunctionBegin;
     64:   PetscAssertPointer(flag, 2);
     65:   *flag = snes->errorifnotconverged;
     66:   PetscFunctionReturn(PETSC_SUCCESS);
     67: }

     69: /*@
     70:   SNESSetAlwaysComputesFinalResidual - tells the `SNES` to always compute the residual (nonlinear function value) at the final solution

     72:   Logically Collective

     74:   Input Parameters:
     75: + snes - the shell `SNES`
     76: - flg  - `PETSC_TRUE` to always compute the residual

     78:   Level: advanced

     80:   Note:
     81:   Some solvers (such as smoothers in a `SNESFAS`) do not need the residual computed at the final solution so skip computing it
     82:   to save time.

     84: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESGetAlwaysComputesFinalResidual()`
     85: @*/
     86: PetscErrorCode SNESSetAlwaysComputesFinalResidual(SNES snes, PetscBool flg)
     87: {
     88:   PetscFunctionBegin;
     90:   snes->alwayscomputesfinalresidual = flg;
     91:   PetscFunctionReturn(PETSC_SUCCESS);
     92: }

     94: /*@
     95:   SNESGetAlwaysComputesFinalResidual - checks if the `SNES` always computes the residual at the final solution

     97:   Logically Collective

     99:   Input Parameter:
    100: . snes - the `SNES` context

    102:   Output Parameter:
    103: . flg - `PETSC_TRUE` if the residual is computed

    105:   Level: advanced

    107: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSolve()`, `SNESSetAlwaysComputesFinalResidual()`
    108: @*/
    109: PetscErrorCode SNESGetAlwaysComputesFinalResidual(SNES snes, PetscBool *flg)
    110: {
    111:   PetscFunctionBegin;
    113:   *flg = snes->alwayscomputesfinalresidual;
    114:   PetscFunctionReturn(PETSC_SUCCESS);
    115: }

    117: /*@
    118:   SNESSetFunctionDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetFunction()` is not
    119:   in the function's domain. For example, a step with negative pressure.

    121:   Not Collective

    123:   Input Parameter:
    124: . snes - the `SNES` context

    126:   Level: advanced

    128:   Notes:
    129:   This does not need to be called by all processes in the `SNES` MPI communicator.

    131:   A few solvers will try to cut the step size to avoid the domain error but for other solvers `SNESSolve()` stops iterating and
    132:   returns with a `SNESConvergedReason` of `SNES_DIVERGED_FUNCTION_DOMAIN`

    134:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    135:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    137:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    139:   You can call `SNESSetJacobianDomainError()` during a Jacobian computation to indicate the proposed solution is not in the domain.

    141:   Developer Note:
    142:   This value is used by `SNESCheckFunctionDomainError()` to determine if the `SNESConvergedReason` is set to `SNES_DIVERGED_FUNCTION_DOMAIN`

    144: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    145:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`,
    146:           `SNES_DIVERGED_FUNCTION_DOMAIN`, `SNESSetObjectiveDomainError()`, `SNES_DIVERGED_OBJECTIVE_DOMAIN`
    147: @*/
    148: PetscErrorCode SNESSetFunctionDomainError(SNES snes)
    149: {
    150:   PetscFunctionBegin;
    152:   snes->functiondomainerror = PETSC_TRUE;
    153:   PetscFunctionReturn(PETSC_SUCCESS);
    154: }

    156: /*@
    157:   SNESSetObjectiveDomainError - tells `SNES` that the input vector, a proposed new solution, to your function you provided to `SNESSetObjective()` is not
    158:   in the function's domain. For example, a step with negative pressure.

    160:   Not Collective

    162:   Input Parameter:
    163: . snes - the `SNES` context

    165:   Level: advanced

    167:   Notes:
    168:   This does not need to be called by all processes in the `SNES` MPI communicator.

    170:   A few solvers will try to cut the step size to avoid the domain error but for other solvers `SNESSolve()` stops iterating and
    171:   returns with a `SNESConvergedReason` of `SNES_DIVERGED_OBJECTIVE_DOMAIN`

    173:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    174:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    176:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    178:   You can call `SNESSetJacobianDomainError()` during a Jacobian computation to indicate the proposed solution is not in the domain.

    180:   Developer Note:
    181:   This value is used by `SNESCheckObjectiveDomainError()` to determine if the `SNESConvergedReason` is set to `SNES_DIVERGED_OBJECTIVE_DOMAIN`

    183: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetJacobianDomainError()`, `SNESVISetVariableBounds()`,
    184:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`,
    185:           `SNES_DIVERGED_OBJECTIVE_DOMAIN`, `SNESSetFunctionDomainError()`, `SNES_DIVERGED_FUNCTION_DOMAIN`
    186: @*/
    187: PetscErrorCode SNESSetObjectiveDomainError(SNES snes)
    188: {
    189:   PetscFunctionBegin;
    191:   snes->objectivedomainerror = PETSC_TRUE;
    192:   PetscFunctionReturn(PETSC_SUCCESS);
    193: }

    195: /*@
    196:   SNESSetJacobianDomainError - tells `SNES` that the function you provided to `SNESSetJacobian()` at the proposed step. For example there is a negative element transformation.

    198:   Logically Collective

    200:   Input Parameter:
    201: . snes - the `SNES` context

    203:   Level: advanced

    205:   Notes:
    206:   If this is called the `SNESSolve()` stops iterating and returns with a `SNESConvergedReason` of `SNES_DIVERGED_JACOBIAN_DOMAIN`

    208:   You should always call `SNESGetConvergedReason()` after each `SNESSolve()` and verify if the iteration converged (positive result) or diverged (negative result).

    210:   You can direct `SNES` to avoid certain steps by using `SNESVISetVariableBounds()`, `SNESVISetComputeVariableBounds()` or
    211:   `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`

    213: .seealso: [](ch_snes), `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESVISetVariableBounds()`,
    214:           `SNESVISetComputeVariableBounds()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESConvergedReason`, `SNESGetConvergedReason()`
    215: @*/
    216: PetscErrorCode SNESSetJacobianDomainError(SNES snes)
    217: {
    218:   PetscFunctionBegin;
    220:   PetscCheck(!snes->errorifnotconverged, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "User code indicates computeJacobian does not make sense");
    221:   snes->jacobiandomainerror = PETSC_TRUE;
    222:   PetscFunctionReturn(PETSC_SUCCESS);
    223: }

    225: /*@
    226:   SNESSetCheckJacobianDomainError - tells `SNESSolve()` whether to check if the user called `SNESSetJacobianDomainError()` to indicate a Jacobian domain error after
    227:   each Jacobian evaluation.

    229:   Logically Collective

    231:   Input Parameters:
    232: + snes - the `SNES` context
    233: - flg  - indicates if or not to check Jacobian domain error after each Jacobian evaluation

    235:   Level: advanced

    237:   Notes:
    238:   By default, it checks for the Jacobian domain error in the debug mode, and does not check it in the optimized mode.

    240:   Checks require one extra parallel synchronization for each Jacobian evaluation

    242: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESGetCheckJacobianDomainError()`
    243: @*/
    244: PetscErrorCode SNESSetCheckJacobianDomainError(SNES snes, PetscBool flg)
    245: {
    246:   PetscFunctionBegin;
    248:   snes->checkjacdomainerror = flg;
    249:   PetscFunctionReturn(PETSC_SUCCESS);
    250: }

    252: /*@
    253:   SNESGetCheckJacobianDomainError - Get an indicator whether or not `SNES` is checking Jacobian domain errors after each Jacobian evaluation.

    255:   Logically Collective

    257:   Input Parameter:
    258: . snes - the `SNES` context

    260:   Output Parameter:
    261: . flg - `PETSC_FALSE` indicates that it is not checking Jacobian domain errors after each Jacobian evaluation

    263:   Level: advanced

    265: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSetFunction()`, `SNESFunctionFn`, `SNESSetFunctionDomainError()`, `SNESSetCheckJacobianDomainError()`
    266: @*/
    267: PetscErrorCode SNESGetCheckJacobianDomainError(SNES snes, PetscBool *flg)
    268: {
    269:   PetscFunctionBegin;
    271:   PetscAssertPointer(flg, 2);
    272:   *flg = snes->checkjacdomainerror;
    273:   PetscFunctionReturn(PETSC_SUCCESS);
    274: }

    276: /*@
    277:   SNESLoad - Loads a `SNES` that has been stored in `PETSCVIEWERBINARY` with `SNESView()`.

    279:   Collective

    281:   Input Parameters:
    282: + snes   - the newly loaded `SNES`, this needs to have been created with `SNESCreate()` or
    283:            some related function before a call to `SNESLoad()`.
    284: - viewer - binary file viewer, obtained from `PetscViewerBinaryOpen()`

    286:   Level: intermediate

    288:   Note:
    289:   The `SNESType` is determined by the data in the file, any type set into the `SNES` before this call is ignored.

    291: .seealso: [](ch_snes), `SNES`, `PetscViewer`, `SNESCreate()`, `SNESType`, `PetscViewerBinaryOpen()`, `SNESView()`, `MatLoad()`, `VecLoad()`
    292: @*/
    293: PetscErrorCode SNESLoad(SNES snes, PetscViewer viewer)
    294: {
    295:   PetscBool isbinary;
    296:   PetscInt  classid;
    297:   char      type[256];
    298:   KSP       ksp;
    299:   DM        dm;
    300:   DMSNES    dmsnes;

    302:   PetscFunctionBegin;
    305:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    306:   PetscCheck(isbinary, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONG, "Invalid viewer; open viewer with PetscViewerBinaryOpen()");

    308:   PetscCall(PetscViewerBinaryRead(viewer, &classid, 1, NULL, PETSC_INT));
    309:   PetscCheck(classid == SNES_FILE_CLASSID, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Not SNES next in file");
    310:   PetscCall(PetscViewerBinaryRead(viewer, type, 256, NULL, PETSC_CHAR));
    311:   PetscCall(SNESSetType(snes, type));
    312:   PetscTryTypeMethod(snes, load, viewer);
    313:   PetscCall(SNESGetDM(snes, &dm));
    314:   PetscCall(DMGetDMSNES(dm, &dmsnes));
    315:   PetscCall(DMSNESLoad(dmsnes, viewer));
    316:   PetscCall(SNESGetKSP(snes, &ksp));
    317:   PetscCall(KSPLoad(ksp, viewer));
    318:   PetscFunctionReturn(PETSC_SUCCESS);
    319: }

    321: #include <petscdraw.h>
    322: #if defined(PETSC_HAVE_SAWS)
    323: #include <petscviewersaws.h>
    324: #endif

    326: /*@
    327:   SNESViewFromOptions - View a `SNES` based on values in the options database

    329:   Collective

    331:   Input Parameters:
    332: + A    - the `SNES` context
    333: . obj  - Optional object that provides the options prefix for the checks
    334: - name - command line option

    336:   Level: intermediate

    338: .seealso: [](ch_snes), `SNES`, `SNESView`, `PetscObjectViewFromOptions()`, `SNESCreate()`
    339: @*/
    340: PetscErrorCode SNESViewFromOptions(SNES A, PetscObject obj, const char name[])
    341: {
    342:   PetscFunctionBegin;
    344:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
    345:   PetscFunctionReturn(PETSC_SUCCESS);
    346: }

    348: PETSC_EXTERN PetscErrorCode SNESComputeJacobian_DMDA(SNES, Vec, Mat, Mat, void *);

    350: /*@
    351:   SNESView - Prints or visualizes the `SNES` data structure.

    353:   Collective

    355:   Input Parameters:
    356: + snes   - the `SNES` context
    357: - viewer - the `PetscViewer`

    359:   Options Database Key:
    360: . -snes_view - Calls `SNESView()` at end of `SNESSolve()`

    362:   Level: beginner

    364:   Notes:
    365:   The available visualization contexts include
    366: +     `PETSC_VIEWER_STDOUT_SELF` - standard output (default)
    367: -     `PETSC_VIEWER_STDOUT_WORLD` - synchronized standard
    368:   output where only the first processor opens
    369:   the file.  All other processors send their
    370:   data to the first processor to print.

    372:   The available formats include
    373: +     `PETSC_VIEWER_DEFAULT` - standard output (default)
    374: -     `PETSC_VIEWER_ASCII_INFO_DETAIL` - more verbose output for `SNESNASM`

    376:   The user can open an alternative visualization context with
    377:   `PetscViewerASCIIOpen()` - output to a specified file.

    379:   In the debugger you can do "call `SNESView`(snes,0)" to display the `SNES` solver. (The same holds for any PETSc object viewer).

    381: .seealso: [](ch_snes), `SNES`, `SNESLoad()`, `SNESCreate()`, `PetscViewerASCIIOpen()`
    382: @*/
    383: PetscErrorCode SNESView(SNES snes, PetscViewer viewer)
    384: {
    385:   SNESKSPEW     *kctx;
    386:   KSP            ksp;
    387:   SNESLineSearch linesearch;
    388:   PetscBool      isascii, isstring, isbinary, isdraw;
    389:   DMSNES         dmsnes;
    390: #if defined(PETSC_HAVE_SAWS)
    391:   PetscBool issaws;
    392: #endif

    394:   PetscFunctionBegin;
    396:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &viewer));
    398:   PetscCheckSameComm(snes, 1, viewer, 2);

    400:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isascii));
    401:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSTRING, &isstring));
    402:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERBINARY, &isbinary));
    403:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERDRAW, &isdraw));
    404: #if defined(PETSC_HAVE_SAWS)
    405:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
    406: #endif
    407:   if (isascii) {
    408:     SNESNormSchedule normschedule;
    409:     DM               dm;
    410:     SNESJacobianFn  *cJ;
    411:     void            *ctx;
    412:     const char      *pre = "";

    414:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)snes, viewer));
    415:     if (!snes->setupcalled) PetscCall(PetscViewerASCIIPrintf(viewer, "  SNES has not been set up so information may be incomplete\n"));
    416:     if (snes->ops->view) {
    417:       PetscCall(PetscViewerASCIIPushTab(viewer));
    418:       PetscUseTypeMethod(snes, view, viewer);
    419:       PetscCall(PetscViewerASCIIPopTab(viewer));
    420:     }
    421:     if (snes->max_funcs == PETSC_UNLIMITED) {
    422:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=unlimited\n", snes->max_its));
    423:     } else {
    424:       PetscCall(PetscViewerASCIIPrintf(viewer, "  maximum iterations=%" PetscInt_FMT ", maximum function evaluations=%" PetscInt_FMT "\n", snes->max_its, snes->max_funcs));
    425:     }
    426:     PetscCall(PetscViewerASCIIPrintf(viewer, "  tolerances: relative=%g, absolute=%g, solution=%g\n", (double)snes->rtol, (double)snes->abstol, (double)snes->stol));
    427:     if (snes->usesksp) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of linear solver iterations=%" PetscInt_FMT "\n", snes->linear_its));
    428:     PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of function evaluations=%" PetscInt_FMT "\n", snes->nfuncs));
    429:     PetscCall(SNESGetNormSchedule(snes, &normschedule));
    430:     if (normschedule > 0) PetscCall(PetscViewerASCIIPrintf(viewer, "  norm schedule %s\n", SNESNormSchedules[normschedule]));
    431:     if (snes->gridsequence) PetscCall(PetscViewerASCIIPrintf(viewer, "  total number of grid sequence refinements=%" PetscInt_FMT "\n", snes->gridsequence));
    432:     if (snes->ksp_ewconv) {
    433:       kctx = (SNESKSPEW *)snes->kspconvctx;
    434:       if (kctx) {
    435:         PetscCall(PetscViewerASCIIPrintf(viewer, "  Eisenstat-Walker computation of KSP relative tolerance (version %" PetscInt_FMT ")\n", kctx->version));
    436:         PetscCall(PetscViewerASCIIPrintf(viewer, "    rtol_0=%g, rtol_max=%g, threshold=%g\n", (double)kctx->rtol_0, (double)kctx->rtol_max, (double)kctx->threshold));
    437:         PetscCall(PetscViewerASCIIPrintf(viewer, "    gamma=%g, alpha=%g, alpha2=%g\n", (double)kctx->gamma, (double)kctx->alpha, (double)kctx->alpha2));
    438:       }
    439:     }
    440:     if (snes->lagpreconditioner == -1) {
    441:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is never rebuilt\n"));
    442:     } else if (snes->lagpreconditioner > 1) {
    443:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Preconditioned is rebuilt every %" PetscInt_FMT " new Jacobians\n", snes->lagpreconditioner));
    444:     }
    445:     if (snes->lagjacobian == -1) {
    446:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is never rebuilt\n"));
    447:     } else if (snes->lagjacobian > 1) {
    448:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is rebuilt every %" PetscInt_FMT " SNES iterations\n", snes->lagjacobian));
    449:     }
    450:     PetscCall(SNESGetDM(snes, &dm));
    451:     PetscCall(DMSNESGetJacobian(dm, &cJ, &ctx));
    452:     if (snes->mf_operator) {
    453:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing\n"));
    454:       pre = "Preconditioning ";
    455:     }
    456:     if (cJ == SNESComputeJacobianDefault) {
    457:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences one column at a time\n", pre));
    458:     } else if (cJ == SNESComputeJacobianDefaultColor) {
    459:       PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using finite differences with coloring\n", pre));
    460:       /* it slightly breaks data encapsulation for access the DMDA information directly */
    461:     } else if (cJ == SNESComputeJacobian_DMDA) {
    462:       MatFDColoring fdcoloring;
    463:       PetscCall(PetscObjectQuery((PetscObject)dm, "DMDASNES_FDCOLORING", (PetscObject *)&fdcoloring));
    464:       if (fdcoloring) {
    465:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using colored finite differences on a DMDA\n", pre));
    466:       } else {
    467:         PetscCall(PetscViewerASCIIPrintf(viewer, "  %sJacobian is built using a DMDA local Jacobian\n", pre));
    468:       }
    469:     } else if (snes->mf && !snes->mf_operator) {
    470:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Jacobian is applied matrix-free with differencing, no explicit Jacobian\n"));
    471:     }
    472:   } else if (isstring) {
    473:     const char *type;
    474:     PetscCall(SNESGetType(snes, &type));
    475:     PetscCall(PetscViewerStringSPrintf(viewer, " SNESType: %-7.7s", type));
    476:     PetscTryTypeMethod(snes, view, viewer);
    477:   } else if (isbinary) {
    478:     PetscInt    classid = SNES_FILE_CLASSID;
    479:     MPI_Comm    comm;
    480:     PetscMPIInt rank;
    481:     char        type[256];

    483:     PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    484:     PetscCallMPI(MPI_Comm_rank(comm, &rank));
    485:     if (rank == 0) {
    486:       PetscCall(PetscViewerBinaryWrite(viewer, &classid, 1, PETSC_INT));
    487:       PetscCall(PetscStrncpy(type, ((PetscObject)snes)->type_name, sizeof(type)));
    488:       PetscCall(PetscViewerBinaryWrite(viewer, type, sizeof(type), PETSC_CHAR));
    489:     }
    490:     PetscTryTypeMethod(snes, view, viewer);
    491:   } else if (isdraw) {
    492:     PetscDraw draw;
    493:     char      str[36];
    494:     PetscReal x, y, bottom, h;

    496:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    497:     PetscCall(PetscDrawGetCurrentPoint(draw, &x, &y));
    498:     PetscCall(PetscStrncpy(str, "SNES: ", sizeof(str)));
    499:     PetscCall(PetscStrlcat(str, ((PetscObject)snes)->type_name, sizeof(str)));
    500:     PetscCall(PetscDrawStringBoxed(draw, x, y, PETSC_DRAW_BLUE, PETSC_DRAW_BLACK, str, NULL, &h));
    501:     bottom = y - h;
    502:     PetscCall(PetscDrawPushCurrentPoint(draw, x, bottom));
    503:     PetscTryTypeMethod(snes, view, viewer);
    504: #if defined(PETSC_HAVE_SAWS)
    505:   } else if (issaws) {
    506:     PetscMPIInt rank;
    507:     const char *name;

    509:     PetscCall(PetscObjectGetName((PetscObject)snes, &name));
    510:     PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    511:     if (!((PetscObject)snes)->amsmem && rank == 0) {
    512:       char dir[1024];

    514:       PetscCall(PetscObjectViewSAWs((PetscObject)snes, viewer));
    515:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/its", name));
    516:       PetscCallSAWs(SAWs_Register, (dir, &snes->iter, 1, SAWs_READ, SAWs_INT));
    517:       if (!snes->conv_hist) PetscCall(SNESSetConvergenceHistory(snes, NULL, NULL, PETSC_DECIDE, PETSC_TRUE));
    518:       PetscCall(PetscSNPrintf(dir, 1024, "/PETSc/Objects/%s/conv_hist", name));
    519:       PetscCallSAWs(SAWs_Register, (dir, snes->conv_hist, 10, SAWs_READ, SAWs_DOUBLE));
    520:     }
    521: #endif
    522:   }
    523:   if (snes->linesearch) {
    524:     PetscCall(SNESGetLineSearch(snes, &linesearch));
    525:     PetscCall(PetscViewerASCIIPushTab(viewer));
    526:     PetscCall(SNESLineSearchView(linesearch, viewer));
    527:     PetscCall(PetscViewerASCIIPopTab(viewer));
    528:   }
    529:   if (snes->npc && snes->usesnpc) {
    530:     PetscCall(PetscViewerASCIIPushTab(viewer));
    531:     PetscCall(SNESView(snes->npc, viewer));
    532:     PetscCall(PetscViewerASCIIPopTab(viewer));
    533:   }
    534:   PetscCall(PetscViewerASCIIPushTab(viewer));
    535:   PetscCall(DMGetDMSNES(snes->dm, &dmsnes));
    536:   PetscCall(DMSNESView(dmsnes, viewer));
    537:   PetscCall(PetscViewerASCIIPopTab(viewer));
    538:   if (snes->usesksp) {
    539:     PetscCall(SNESGetKSP(snes, &ksp));
    540:     PetscCall(PetscViewerASCIIPushTab(viewer));
    541:     PetscCall(KSPView(ksp, viewer));
    542:     PetscCall(PetscViewerASCIIPopTab(viewer));
    543:   }
    544:   if (isdraw) {
    545:     PetscDraw draw;
    546:     PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
    547:     PetscCall(PetscDrawPopCurrentPoint(draw));
    548:   }
    549:   PetscFunctionReturn(PETSC_SUCCESS);
    550: }

    552: /*
    553:   We retain a list of functions that also take SNES command
    554:   line options. These are called at the end SNESSetFromOptions()
    555: */
    556: #define MAXSETFROMOPTIONS 5
    557: static PetscInt numberofsetfromoptions;
    558: static PetscErrorCode (*othersetfromoptions[MAXSETFROMOPTIONS])(SNES);

    560: /*@C
    561:   SNESAddOptionsChecker - Adds an additional function to check for `SNES` options.

    563:   Not Collective

    565:   Input Parameter:
    566: . snescheck - function that checks for options

    568:   Calling sequence of `snescheck`:
    569: . snes - the `SNES` object for which it is checking options

    571:   Level: developer

    573: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`
    574: @*/
    575: PetscErrorCode SNESAddOptionsChecker(PetscErrorCode (*snescheck)(SNES snes))
    576: {
    577:   PetscFunctionBegin;
    578:   PetscCheck(numberofsetfromoptions < MAXSETFROMOPTIONS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many options checkers, only %d allowed", MAXSETFROMOPTIONS);
    579:   othersetfromoptions[numberofsetfromoptions++] = snescheck;
    580:   PetscFunctionReturn(PETSC_SUCCESS);
    581: }

    583: static PetscErrorCode SNESSetUpMatrixFree_Private(SNES snes, PetscBool hasOperator, PetscInt version)
    584: {
    585:   Mat          J;
    586:   MatNullSpace nullsp;

    588:   PetscFunctionBegin;

    591:   if (!snes->vec_func && (snes->jacobian || snes->jacobian_pre)) {
    592:     Mat A = snes->jacobian, B = snes->jacobian_pre;
    593:     PetscCall(MatCreateVecs(A ? A : B, NULL, &snes->vec_func));
    594:   }

    596:   PetscCheck(version == 1 || version == 2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "matrix-free operator routines, only version 1 and 2");
    597:   if (version == 1) {
    598:     PetscCall(MatCreateSNESMF(snes, &J));
    599:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    600:     PetscCall(MatSetFromOptions(J));
    601:     /* TODO: the version 2 code should be merged into the MatCreateSNESMF() and MatCreateMFFD() infrastructure and then removed */
    602:   } else /* if (version == 2) */ {
    603:     PetscCheck(snes->vec_func, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "SNESSetFunction() must be called first");
    604: #if !defined(PETSC_USE_COMPLEX) && !defined(PETSC_USE_REAL_SINGLE) && !defined(PETSC_USE_REAL___FLOAT128) && !defined(PETSC_USE_REAL___FP16)
    605:     PetscCall(MatCreateSNESMFMore(snes, snes->vec_func, &J));
    606: #else
    607:     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "matrix-free operator routines (version 2)");
    608: #endif
    609:   }

    611:   /* attach any user provided null space that was on Amat to the newly created matrix-free matrix */
    612:   if (snes->jacobian) {
    613:     PetscCall(MatGetNullSpace(snes->jacobian, &nullsp));
    614:     if (nullsp) PetscCall(MatSetNullSpace(J, nullsp));
    615:   }

    617:   PetscCall(PetscInfo(snes, "Setting default matrix-free operator routines (version %" PetscInt_FMT ")\n", version));
    618:   if (hasOperator) {
    619:     /* This version replaces the user provided Jacobian matrix with a
    620:        matrix-free version but still employs the user-provided matrix used for computing the preconditioner. */
    621:     PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    622:   } else {
    623:     /* This version replaces both the user-provided Jacobian and the user-
    624:      provided preconditioner Jacobian with the default matrix-free version. */
    625:     if (snes->npcside == PC_LEFT && snes->npc) {
    626:       if (!snes->jacobian) PetscCall(SNESSetJacobian(snes, J, NULL, NULL, NULL));
    627:     } else {
    628:       KSP       ksp;
    629:       PC        pc;
    630:       PetscBool match;

    632:       PetscCall(SNESSetJacobian(snes, J, J, MatMFFDComputeJacobian, NULL));
    633:       /* Force no preconditioner */
    634:       PetscCall(SNESGetKSP(snes, &ksp));
    635:       PetscCall(KSPGetPC(ksp, &pc));
    636:       PetscCall(PetscObjectTypeCompareAny((PetscObject)pc, &match, PCSHELL, PCH2OPUS, ""));
    637:       if (!match) {
    638:         PetscCall(PetscInfo(snes, "Setting default matrix-free preconditioner routines\nThat is no preconditioner is being used\n"));
    639:         PetscCall(PCSetType(pc, PCNONE));
    640:       }
    641:     }
    642:   }
    643:   PetscCall(MatDestroy(&J));
    644:   PetscFunctionReturn(PETSC_SUCCESS);
    645: }

    647: static PetscErrorCode DMRestrictHook_SNESVecSol(DM dmfine, Mat Restrict, Vec Rscale, Mat Inject, DM dmcoarse, PetscCtx ctx)
    648: {
    649:   SNES snes = (SNES)ctx;
    650:   Vec  Xfine, Xfine_named = NULL, Xcoarse;

    652:   PetscFunctionBegin;
    653:   if (PetscLogPrintInfo) {
    654:     PetscInt finelevel, coarselevel, fineclevel, coarseclevel;
    655:     PetscCall(DMGetRefineLevel(dmfine, &finelevel));
    656:     PetscCall(DMGetCoarsenLevel(dmfine, &fineclevel));
    657:     PetscCall(DMGetRefineLevel(dmcoarse, &coarselevel));
    658:     PetscCall(DMGetCoarsenLevel(dmcoarse, &coarseclevel));
    659:     PetscCall(PetscInfo(dmfine, "Restricting SNES solution vector from level %" PetscInt_FMT "-%" PetscInt_FMT " to level %" PetscInt_FMT "-%" PetscInt_FMT "\n", finelevel, fineclevel, coarselevel, coarseclevel));
    660:   }
    661:   if (dmfine == snes->dm) Xfine = snes->vec_sol;
    662:   else {
    663:     PetscCall(DMGetNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    664:     Xfine = Xfine_named;
    665:   }
    666:   PetscCall(DMGetNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    667:   if (Inject) {
    668:     PetscCall(MatRestrict(Inject, Xfine, Xcoarse));
    669:   } else {
    670:     PetscCall(MatRestrict(Restrict, Xfine, Xcoarse));
    671:     PetscCall(VecPointwiseMult(Xcoarse, Xcoarse, Rscale));
    672:   }
    673:   PetscCall(DMRestoreNamedGlobalVector(dmcoarse, "SNESVecSol", &Xcoarse));
    674:   if (Xfine_named) PetscCall(DMRestoreNamedGlobalVector(dmfine, "SNESVecSol", &Xfine_named));
    675:   PetscFunctionReturn(PETSC_SUCCESS);
    676: }

    678: static PetscErrorCode DMCoarsenHook_SNESVecSol(DM dm, DM dmc, PetscCtx ctx)
    679: {
    680:   PetscFunctionBegin;
    681:   PetscCall(DMCoarsenHookAdd(dmc, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, ctx));
    682:   PetscFunctionReturn(PETSC_SUCCESS);
    683: }

    685: /* This may be called to rediscretize the operator on levels of linear multigrid. The DM shuffle is so the user can
    686:  * safely call SNESGetDM() in their residual evaluation routine. */
    687: static PetscErrorCode KSPComputeOperators_SNES(KSP ksp, Mat A, Mat B, PetscCtx ctx)
    688: {
    689:   SNES            snes = (SNES)ctx;
    690:   DMSNES          sdm;
    691:   Vec             X, Xnamed = NULL;
    692:   DM              dmsave;
    693:   void           *ctxsave;
    694:   SNESJacobianFn *jac = NULL;

    696:   PetscFunctionBegin;
    697:   dmsave = snes->dm;
    698:   PetscCall(KSPGetDM(ksp, &snes->dm));
    699:   if (dmsave == snes->dm) X = snes->vec_sol; /* We are on the finest level */
    700:   else {
    701:     PetscBool has;

    703:     /* We are on a coarser level, this vec was initialized using a DM restrict hook */
    704:     PetscCall(DMHasNamedGlobalVector(snes->dm, "SNESVecSol", &has));
    705:     PetscCheck(has, PetscObjectComm((PetscObject)snes->dm), PETSC_ERR_PLIB, "Missing SNESVecSol");
    706:     PetscCall(DMGetNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    707:     X = Xnamed;
    708:     PetscCall(SNESGetJacobian(snes, NULL, NULL, &jac, &ctxsave));
    709:     /* If the DM's don't match up, the MatFDColoring context needed for the jacobian won't match up either -- fixit. */
    710:     if (jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, SNESComputeJacobianDefaultColor, NULL));
    711:   }

    713:   /* Compute the operators */
    714:   PetscCall(DMGetDMSNES(snes->dm, &sdm));
    715:   if (Xnamed && sdm->ops->computefunction) {
    716:     /* The SNES contract with the user is that ComputeFunction is always called before ComputeJacobian.
    717:        We make sure of this here. Disable affine shift since it is for the finest level */
    718:     Vec F, saverhs = snes->vec_rhs;

    720:     snes->vec_rhs = NULL;
    721:     PetscCall(DMGetGlobalVector(snes->dm, &F));
    722:     PetscCall(SNESComputeFunction(snes, X, F));
    723:     PetscCall(DMRestoreGlobalVector(snes->dm, &F));
    724:     snes->vec_rhs = saverhs;
    725:     snes->nfuncs--; /* Do not log coarser level evaluations */
    726:   }
    727:   /* Make sure KSP DM has the Jacobian computation routine */
    728:   if (!sdm->ops->computejacobian) PetscCall(DMCopyDMSNES(dmsave, snes->dm));
    729:   PetscCall(SNESComputeJacobian(snes, X, A, B)); /* cannot handle previous SNESSetJacobianDomainError() calls */

    731:   /* Put the previous context back */
    732:   if (snes->dm != dmsave && jac == SNESComputeJacobianDefaultColor) PetscCall(SNESSetJacobian(snes, NULL, NULL, jac, ctxsave));

    734:   if (Xnamed) PetscCall(DMRestoreNamedGlobalVector(snes->dm, "SNESVecSol", &Xnamed));
    735:   snes->dm = dmsave;
    736:   PetscFunctionReturn(PETSC_SUCCESS);
    737: }

    739: /*@
    740:   SNESSetUpMatrices - ensures that matrices are available for `SNES` Newton-like methods, this is called by `SNESSetUp_XXX()`

    742:   Collective

    744:   Input Parameter:
    745: . snes - `SNES` object to configure

    747:   Level: developer

    749:   Note:
    750:   If the matrices do not yet exist it attempts to create them based on options previously set for the `SNES` such as `-snes_mf`

    752:   Developer Note:
    753:   The functionality of this routine overlaps in a confusing way with the functionality of `SNESSetUpMatrixFree_Private()` which is called by
    754:   `SNESSetUp()` but sometimes `SNESSetUpMatrices()` is called without `SNESSetUp()` being called. A refactorization to simplify the
    755:   logic that handles the matrix-free case is desirable.

    757: .seealso: [](ch_snes), `SNES`, `SNESSetUp()`
    758: @*/
    759: PetscErrorCode SNESSetUpMatrices(SNES snes)
    760: {
    761:   DM     dm;
    762:   DMSNES sdm;

    764:   PetscFunctionBegin;
    765:   PetscCall(SNESGetDM(snes, &dm));
    766:   PetscCall(DMGetDMSNES(dm, &sdm));
    767:   if (!snes->jacobian && snes->mf && !snes->mf_operator && !snes->jacobian_pre) {
    768:     Mat   J;
    769:     void *functx;
    770:     PetscCall(MatCreateSNESMF(snes, &J));
    771:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    772:     PetscCall(MatSetFromOptions(J));
    773:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    774:     PetscCall(SNESSetJacobian(snes, J, J, NULL, NULL));
    775:     PetscCall(MatDestroy(&J));
    776:   } else if (snes->mf_operator && !snes->jacobian_pre && !snes->jacobian) {
    777:     Mat J, B;
    778:     PetscCall(MatCreateSNESMF(snes, &J));
    779:     PetscCall(MatMFFDSetOptionsPrefix(J, ((PetscObject)snes)->prefix));
    780:     PetscCall(MatSetFromOptions(J));
    781:     PetscCall(DMCreateMatrix(snes->dm, &B));
    782:     /* sdm->computejacobian was already set to reach here */
    783:     PetscCall(SNESSetJacobian(snes, J, B, NULL, NULL));
    784:     PetscCall(MatDestroy(&J));
    785:     PetscCall(MatDestroy(&B));
    786:   } else if (!snes->jacobian_pre) {
    787:     PetscDS   prob;
    788:     Mat       J, B;
    789:     PetscBool hasPrec = PETSC_FALSE;

    791:     J = snes->jacobian;
    792:     PetscCall(DMGetDS(dm, &prob));
    793:     if (prob) PetscCall(PetscDSHasJacobianPreconditioner(prob, &hasPrec));
    794:     if (!J && hasPrec) PetscCall(DMCreateMatrix(snes->dm, &J));
    795:     else PetscCall(PetscObjectReference((PetscObject)J));
    796:     PetscCall(DMCreateMatrix(snes->dm, &B));
    797:     PetscCall(SNESSetJacobian(snes, J ? J : B, B, NULL, NULL));
    798:     PetscCall(MatDestroy(&J));
    799:     PetscCall(MatDestroy(&B));
    800:   }
    801:   {
    802:     KSP ksp;
    803:     PetscCall(SNESGetKSP(snes, &ksp));
    804:     PetscCall(KSPSetComputeOperators(ksp, KSPComputeOperators_SNES, snes));
    805:     PetscCall(DMCoarsenHookAdd(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    806:   }
    807:   PetscFunctionReturn(PETSC_SUCCESS);
    808: }

    810: PETSC_SINGLE_LIBRARY_INTERN PetscErrorCode PetscMonitorPauseFinal_Internal(PetscInt, PetscCtx);

    812: static PetscErrorCode SNESMonitorPauseFinal_Internal(SNES snes)
    813: {
    814:   PetscFunctionBegin;
    815:   if (!snes->pauseFinal) PetscFunctionReturn(PETSC_SUCCESS);
    816:   PetscCall(PetscMonitorPauseFinal_Internal(snes->numbermonitors, snes->monitorcontext));
    817:   PetscFunctionReturn(PETSC_SUCCESS);
    818: }

    820: /*@C
    821:   SNESMonitorSetFromOptions - Sets a monitor function and viewer appropriate for the type indicated by the user

    823:   Collective

    825:   Input Parameters:
    826: + snes         - `SNES` object you wish to monitor
    827: . name         - the monitor type one is seeking
    828: . help         - message indicating what monitoring is done
    829: . manual       - manual page for the monitor
    830: . monitor      - the monitor function, this must use a `PetscViewerFormat` as its context
    831: - monitorsetup - a function that is called once ONLY if the user selected this monitor that may set additional features of the `SNES` or `PetscViewer` objects

    833:   Calling sequence of `monitor`:
    834: + snes - the nonlinear solver context
    835: . it   - the current iteration
    836: . r    - the current function norm
    837: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    839:   Calling sequence of `monitorsetup`:
    840: + snes - the nonlinear solver context
    841: - vf   - a `PetscViewerAndFormat` struct that contains the `PetscViewer` and `PetscViewerFormat` to use

    843:   Options Database Key:
    844: . -name - trigger the use of this monitor in `SNESSetFromOptions()`

    846:   Level: advanced

    848: .seealso: [](ch_snes), `PetscOptionsCreateViewer()`, `PetscOptionsGetReal()`, `PetscOptionsHasName()`, `PetscOptionsGetString()`,
    849:           `PetscOptionsGetIntArray()`, `PetscOptionsGetRealArray()`, `PetscOptionsBool()`,
    850:           `PetscOptionsInt()`, `PetscOptionsString()`, `PetscOptionsReal()`,
    851:           `PetscOptionsName()`, `PetscOptionsBegin()`, `PetscOptionsEnd()`, `PetscOptionsHeadBegin()`,
    852:           `PetscOptionsStringArray()`, `PetscOptionsRealArray()`, `PetscOptionsScalar()`,
    853:           `PetscOptionsBoolGroupBegin()`, `PetscOptionsBoolGroup()`, `PetscOptionsBoolGroupEnd()`,
    854:           `PetscOptionsFList()`, `PetscOptionsEList()`
    855: @*/
    856: PetscErrorCode SNESMonitorSetFromOptions(SNES snes, const char name[], const char help[], const char manual[], PetscErrorCode (*monitor)(SNES snes, PetscInt it, PetscReal r, PetscViewerAndFormat *vf), PetscErrorCode (*monitorsetup)(SNES snes, PetscViewerAndFormat *vf))
    857: {
    858:   PetscViewer       viewer;
    859:   PetscViewerFormat format;
    860:   PetscBool         flg;

    862:   PetscFunctionBegin;
    863:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, name, &viewer, &format, &flg));
    864:   if (flg) {
    865:     PetscViewerAndFormat *vf;
    866:     PetscCall(PetscViewerAndFormatCreate(viewer, format, &vf));
    867:     PetscCall(PetscViewerDestroy(&viewer));
    868:     if (monitorsetup) PetscCall((*monitorsetup)(snes, vf));
    869:     PetscCall(SNESMonitorSet(snes, (PetscErrorCode (*)(SNES, PetscInt, PetscReal, PetscCtx))monitor, vf, (PetscCtxDestroyFn *)PetscViewerAndFormatDestroy));
    870:   }
    871:   PetscFunctionReturn(PETSC_SUCCESS);
    872: }

    874: PetscErrorCode SNESEWSetFromOptions_Private(SNESKSPEW *kctx, PetscBool print_api, MPI_Comm comm, const char *prefix)
    875: {
    876:   const char *api = print_api ? "SNESKSPSetParametersEW" : NULL;

    878:   PetscFunctionBegin;
    879:   PetscOptionsBegin(comm, prefix, "Eisenstat and Walker type forcing options", "KSP");
    880:   PetscCall(PetscOptionsInt("-ksp_ew_version", "Version 1, 2 or 3", api, kctx->version, &kctx->version, NULL));
    881:   PetscCall(PetscOptionsReal("-ksp_ew_rtol0", "0 <= rtol0 < 1", api, kctx->rtol_0, &kctx->rtol_0, NULL));
    882:   kctx->rtol_max = PetscMax(kctx->rtol_0, kctx->rtol_max);
    883:   PetscCall(PetscOptionsReal("-ksp_ew_rtolmax", "0 <= rtolmax < 1", api, kctx->rtol_max, &kctx->rtol_max, NULL));
    884:   PetscCall(PetscOptionsReal("-ksp_ew_gamma", "0 <= gamma <= 1", api, kctx->gamma, &kctx->gamma, NULL));
    885:   PetscCall(PetscOptionsReal("-ksp_ew_alpha", "1 < alpha <= 2", api, kctx->alpha, &kctx->alpha, NULL));
    886:   PetscCall(PetscOptionsReal("-ksp_ew_alpha2", "alpha2", NULL, kctx->alpha2, &kctx->alpha2, NULL));
    887:   PetscCall(PetscOptionsReal("-ksp_ew_threshold", "0 < threshold < 1", api, kctx->threshold, &kctx->threshold, NULL));
    888:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p1", "p1", NULL, kctx->v4_p1, &kctx->v4_p1, NULL));
    889:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p2", "p2", NULL, kctx->v4_p2, &kctx->v4_p2, NULL));
    890:   PetscCall(PetscOptionsReal("-ksp_ew_v4_p3", "p3", NULL, kctx->v4_p3, &kctx->v4_p3, NULL));
    891:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m1", "Scaling when rk-1 in [p2,p3)", NULL, kctx->v4_m1, &kctx->v4_m1, NULL));
    892:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m2", "Scaling when rk-1 in [p3,+infty)", NULL, kctx->v4_m2, &kctx->v4_m2, NULL));
    893:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m3", "Threshold for successive rtol (0.1 in Eq.7)", NULL, kctx->v4_m3, &kctx->v4_m3, NULL));
    894:   PetscCall(PetscOptionsReal("-ksp_ew_v4_m4", "Adaptation scaling (0.5 in Eq.7)", NULL, kctx->v4_m4, &kctx->v4_m4, NULL));
    895:   PetscOptionsEnd();
    896:   PetscFunctionReturn(PETSC_SUCCESS);
    897: }

    899: /*@
    900:   SNESSetFromOptions - Sets various `SNES` and `KSP` parameters from user options.

    902:   Collective

    904:   Input Parameter:
    905: . snes - the `SNES` context

    907:   Options Database Keys:
    908: + -snes_type type                                                              - newtonls, newtontr, ngmres, ncg, nrichardson, qn, vi, fas, `SNESType` for complete list
    909: . -snes_rtol rtol                                                              - relative decrease in tolerance norm from initial
    910: . -snes_atol abstol                                                            - absolute tolerance of residual norm
    911: . -snes_stol stol                                                              - convergence tolerance in terms of the norm of the change in the solution between steps
    912: . -snes_divergence_tolerance divtol                                            - if the residual goes above divtol*rnorm0, exit with divergence
    913: . -snes_max_it max_it                                                          - maximum number of iterations
    914: . -snes_max_funcs max_funcs                                                    - maximum number of function evaluations
    915: . -snes_force_iteration force                                                  - force `SNESSolve()` to take at least one iteration
    916: . -snes_max_fail max_fail                                                      - maximum number of line search failures allowed before stopping, default is none
    917: . -snes_max_linear_solve_fail                                                  - number of linear solver failures before SNESSolve() stops
    918: . -snes_lag_preconditioner lag                                                 - how often preconditioner is rebuilt (use -1 to never rebuild)
    919: . -snes_lag_preconditioner_persists (true|false)                               - retains the -snes_lag_preconditioner information across multiple SNESSolve()
    920: . -snes_lag_jacobian lag                                                       - how often Jacobian is rebuilt (use -1 to never rebuild)
    921: . -snes_lag_jacobian_persists (true|false)                                     - retains the -snes_lag_jacobian information across multiple SNESSolve()
    922: . -snes_convergence_test (default|skip|correct_pressure)                       - convergence test in nonlinear solver. default `SNESConvergedDefault()`. skip `SNESConvergedSkip()` means continue
    923:                                                                                  iterating until max_it or some other criterion is reached, saving expense of convergence test. correct_pressure
    924:                                                                                  `SNESConvergedCorrectPressure()` has special handling of a pressure null space.
    925: . -snes_monitor [ascii][:filename][:viewer format]                             - prints residual norm at each iteration. if no filename given prints to stdout
    926: . -snes_monitor_solution [ascii binary draw][:filename][:viewer format]        - plots solution at each iteration
    927: . -snes_monitor_residual [ascii binary draw][:filename][:viewer format]        - plots residual (not its norm) at each iteration
    928: . -snes_monitor_solution_update [ascii binary draw][:filename][:viewer format] - plots update to solution at each iteration
    929: . -snes_monitor_lg_residualnorm                                                - plots residual norm at each iteration
    930: . -snes_monitor_lg_range                                                       - plots residual norm at each iteration
    931: . -snes_monitor_pause_final                                                    - Pauses all monitor drawing after the solver ends
    932: . -snes_fd                                                                     - use finite differences to compute Jacobian; very slow, only for testing
    933: . -snes_fd_color                                                               - use finite differences with coloring to compute Jacobian
    934: . -snes_mf_ksp_monitor                                                         - if using matrix-free multiply then print h at each `KSP` iteration
    935: . -snes_converged_reason                                                       - print the reason for convergence/divergence after each solve
    936: . -npc_snes_type type                                                          - the `SNES` type to use as a nonlinear preconditioner
    937: . -snes_test_jacobian [threshold]                                              - compare the user provided Jacobian with one computed via finite differences to check for errors.
    938:                                                                                  If a threshold is given, display only those entries whose difference is greater than the threshold.
    939: - -snes_test_jacobian_view                                                     - display the user provided Jacobian, the finite difference Jacobian and the difference between them
    940:                                                                                  to help users detect the location of errors in the user provided Jacobian.

    942:   Options Database Keys for Eisenstat-Walker method:
    943: + -snes_ksp_ew                     - use Eisenstat-Walker method for determining linear system convergence
    944: . -snes_ksp_ew_version ver         - version of  Eisenstat-Walker method
    945: . -snes_ksp_ew_rtol0 rtol0         - Sets rtol0
    946: . -snes_ksp_ew_rtolmax rtolmax     - Sets rtolmax
    947: . -snes_ksp_ew_gamma gamma         - Sets gamma
    948: . -snes_ksp_ew_alpha alpha         - Sets alpha
    949: . -snes_ksp_ew_alpha2 alpha2       - Sets alpha2
    950: - -snes_ksp_ew_threshold threshold - Sets threshold

    952:   Level: beginner

    954:   Notes:
    955:   To see all options, run your program with the -help option or consult the users manual

    957:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    958:   and computing explicitly with
    959:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    961: .seealso: [](ch_snes), `SNESType`, `SNESSetOptionsPrefix()`, `SNESResetFromOptions()`, `SNES`, `SNESCreate()`, `MatCreateSNESMF()`, `MatFDColoring`
    962: @*/
    963: PetscErrorCode SNESSetFromOptions(SNES snes)
    964: {
    965:   PetscBool   flg, pcset, persist, set;
    966:   PetscInt    i, indx, lag, grids, max_its, max_funcs;
    967:   const char *deft        = SNESNEWTONLS;
    968:   const char *convtests[] = {"default", "skip", "correct_pressure"};
    969:   SNESKSPEW  *kctx        = NULL;
    970:   char        type[256], monfilename[PETSC_MAX_PATH_LEN], ewprefix[256];
    971:   PCSide      pcside;
    972:   const char *optionsprefix;
    973:   PetscReal   rtol, abstol, stol;

    975:   PetscFunctionBegin;
    977:   PetscCall(SNESRegisterAll());
    978:   PetscObjectOptionsBegin((PetscObject)snes);
    979:   if (((PetscObject)snes)->type_name) deft = ((PetscObject)snes)->type_name;
    980:   PetscCall(PetscOptionsFList("-snes_type", "Nonlinear solver method", "SNESSetType", SNESList, deft, type, 256, &flg));
    981:   if (flg) PetscCall(SNESSetType(snes, type));
    982:   else if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, deft));

    984:   abstol    = snes->abstol;
    985:   rtol      = snes->rtol;
    986:   stol      = snes->stol;
    987:   max_its   = snes->max_its;
    988:   max_funcs = snes->max_funcs;
    989:   PetscCall(PetscOptionsReal("-snes_rtol", "Stop if decrease in function norm less than", "SNESSetTolerances", snes->rtol, &rtol, NULL));
    990:   PetscCall(PetscOptionsReal("-snes_atol", "Stop if function norm less than", "SNESSetTolerances", snes->abstol, &abstol, NULL));
    991:   PetscCall(PetscOptionsReal("-snes_stol", "Stop if step length less than", "SNESSetTolerances", snes->stol, &stol, NULL));
    992:   PetscCall(PetscOptionsInt("-snes_max_it", "Maximum iterations", "SNESSetTolerances", snes->max_its, &max_its, NULL));
    993:   PetscCall(PetscOptionsInt("-snes_max_funcs", "Maximum function evaluations", "SNESSetTolerances", snes->max_funcs, &max_funcs, NULL));
    994:   PetscCall(SNESSetTolerances(snes, abstol, rtol, stol, max_its, max_funcs));

    996:   PetscCall(PetscOptionsReal("-snes_divergence_tolerance", "Stop if residual norm increases by this factor", "SNESSetDivergenceTolerance", snes->divtol, &snes->divtol, &flg));
    997:   if (flg) PetscCall(SNESSetDivergenceTolerance(snes, snes->divtol));

    999:   PetscCall(PetscOptionsInt("-snes_max_fail", "Maximum nonlinear step failures", "SNESSetMaxNonlinearStepFailures", snes->maxFailures, &snes->maxFailures, &flg));
    1000:   if (flg) PetscCall(SNESSetMaxNonlinearStepFailures(snes, snes->maxFailures));

    1002:   PetscCall(PetscOptionsInt("-snes_max_linear_solve_fail", "Maximum failures in linear solves allowed", "SNESSetMaxLinearSolveFailures", snes->maxLinearSolveFailures, &snes->maxLinearSolveFailures, &flg));
    1003:   if (flg) PetscCall(SNESSetMaxLinearSolveFailures(snes, snes->maxLinearSolveFailures));

    1005:   PetscCall(PetscOptionsBool("-snes_error_if_not_converged", "Generate error if solver does not converge", "SNESSetErrorIfNotConverged", snes->errorifnotconverged, &snes->errorifnotconverged, NULL));
    1006:   PetscCall(PetscOptionsBool("-snes_force_iteration", "Force SNESSolve() to take at least one iteration", "SNESSetForceIteration", snes->forceiteration, &snes->forceiteration, NULL));
    1007:   PetscCall(PetscOptionsBool("-snes_check_jacobian_domain_error", "Check Jacobian domain error after Jacobian evaluation", "SNESCheckJacobianDomainError", snes->checkjacdomainerror, &snes->checkjacdomainerror, NULL));

    1009:   PetscCall(PetscOptionsInt("-snes_lag_preconditioner", "How often to rebuild preconditioner", "SNESSetLagPreconditioner", snes->lagpreconditioner, &lag, &flg));
    1010:   if (flg) {
    1011:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the preconditioner must be built as least once, perhaps you mean -2");
    1012:     PetscCall(SNESSetLagPreconditioner(snes, lag));
    1013:   }
    1014:   PetscCall(PetscOptionsBool("-snes_lag_preconditioner_persists", "Preconditioner lagging through multiple SNES solves", "SNESSetLagPreconditionerPersists", snes->lagjac_persist, &persist, &flg));
    1015:   if (flg) PetscCall(SNESSetLagPreconditionerPersists(snes, persist));
    1016:   PetscCall(PetscOptionsInt("-snes_lag_jacobian", "How often to rebuild Jacobian", "SNESSetLagJacobian", snes->lagjacobian, &lag, &flg));
    1017:   if (flg) {
    1018:     PetscCheck(lag != -1, PetscObjectComm((PetscObject)snes), PETSC_ERR_USER, "Cannot set the lag to -1 from the command line since the Jacobian must be built as least once, perhaps you mean -2");
    1019:     PetscCall(SNESSetLagJacobian(snes, lag));
    1020:   }
    1021:   PetscCall(PetscOptionsBool("-snes_lag_jacobian_persists", "Jacobian lagging through multiple SNES solves", "SNESSetLagJacobianPersists", snes->lagjac_persist, &persist, &flg));
    1022:   if (flg) PetscCall(SNESSetLagJacobianPersists(snes, persist));

    1024:   PetscCall(PetscOptionsInt("-snes_grid_sequence", "Use grid sequencing to generate initial guess", "SNESSetGridSequence", snes->gridsequence, &grids, &flg));
    1025:   if (flg) PetscCall(SNESSetGridSequence(snes, grids));

    1027:   PetscCall(PetscOptionsEList("-snes_convergence_test", "Convergence test", "SNESSetConvergenceTest", convtests, PETSC_STATIC_ARRAY_LENGTH(convtests), "default", &indx, &flg));
    1028:   if (flg) {
    1029:     switch (indx) {
    1030:     case 0:
    1031:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedDefault, NULL, NULL));
    1032:       break;
    1033:     case 1:
    1034:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedSkip, NULL, NULL));
    1035:       break;
    1036:     case 2:
    1037:       PetscCall(SNESSetConvergenceTest(snes, SNESConvergedCorrectPressure, NULL, NULL));
    1038:       break;
    1039:     }
    1040:   }

    1042:   PetscCall(PetscOptionsEList("-snes_norm_schedule", "SNES Norm schedule", "SNESSetNormSchedule", SNESNormSchedules, 5, "function", &indx, &flg));
    1043:   if (flg) PetscCall(SNESSetNormSchedule(snes, (SNESNormSchedule)indx));

    1045:   PetscCall(PetscOptionsEList("-snes_function_type", "SNES Norm schedule", "SNESSetFunctionType", SNESFunctionTypes, 2, "unpreconditioned", &indx, &flg));
    1046:   if (flg) PetscCall(SNESSetFunctionType(snes, (SNESFunctionType)indx));

    1048:   kctx = (SNESKSPEW *)snes->kspconvctx;

    1050:   PetscCall(PetscOptionsBool("-snes_ksp_ew", "Use Eisentat-Walker linear system convergence test", "SNESKSPSetUseEW", snes->ksp_ewconv, &snes->ksp_ewconv, NULL));

    1052:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1053:   PetscCall(PetscSNPrintf(ewprefix, sizeof(ewprefix), "%s%s", optionsprefix ? optionsprefix : "", "snes_"));
    1054:   PetscCall(SNESEWSetFromOptions_Private(kctx, PETSC_TRUE, PetscObjectComm((PetscObject)snes), ewprefix));

    1056:   flg = PETSC_FALSE;
    1057:   PetscCall(PetscOptionsBool("-snes_monitor_cancel", "Remove all monitors", "SNESMonitorCancel", flg, &flg, &set));
    1058:   if (set && flg) PetscCall(SNESMonitorCancel(snes));

    1060:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor", "Monitor norm of function", "SNESMonitorDefault", SNESMonitorDefault, SNESMonitorDefaultSetUp));
    1061:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_short", "Monitor norm of function with fewer digits", "SNESMonitorDefaultShort", SNESMonitorDefaultShort, NULL));
    1062:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_range", "Monitor range of elements of function", "SNESMonitorRange", SNESMonitorRange, NULL));

    1064:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_ratio", "Monitor ratios of the norm of function for consecutive steps", "SNESMonitorRatio", SNESMonitorRatio, SNESMonitorRatioSetUp));
    1065:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_field", "Monitor norm of function (split into fields)", "SNESMonitorDefaultField", SNESMonitorDefaultField, NULL));
    1066:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution", "View solution at each iteration", "SNESMonitorSolution", SNESMonitorSolution, NULL));
    1067:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_solution_update", "View correction at each iteration", "SNESMonitorSolutionUpdate", SNESMonitorSolutionUpdate, NULL));
    1068:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_residual", "View residual at each iteration", "SNESMonitorResidual", SNESMonitorResidual, NULL));
    1069:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_jacupdate_spectrum", "Print the change in the spectrum of the Jacobian", "SNESMonitorJacUpdateSpectrum", SNESMonitorJacUpdateSpectrum, NULL));
    1070:   PetscCall(SNESMonitorSetFromOptions(snes, "-snes_monitor_fields", "Monitor norm of function per field", "SNESMonitorSet", SNESMonitorFields, NULL));
    1071:   PetscCall(PetscOptionsBool("-snes_monitor_pause_final", "Pauses all draw monitors at the final iterate", "SNESMonitorPauseFinal_Internal", PETSC_FALSE, &snes->pauseFinal, NULL));

    1073:   PetscCall(PetscOptionsString("-snes_monitor_python", "Use Python function", "SNESMonitorSet", NULL, monfilename, sizeof(monfilename), &flg));
    1074:   if (flg) PetscCall(PetscPythonMonitorSet((PetscObject)snes, monfilename));

    1076:   flg = PETSC_FALSE;
    1077:   PetscCall(PetscOptionsBool("-snes_monitor_lg_range", "Plot function range at each iteration", "SNESMonitorLGRange", flg, &flg, NULL));
    1078:   if (flg) {
    1079:     PetscViewer ctx;

    1081:     PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, NULL, PETSC_DECIDE, PETSC_DECIDE, 400, 300, &ctx));
    1082:     PetscCall(SNESMonitorSet(snes, SNESMonitorLGRange, ctx, (PetscCtxDestroyFn *)PetscViewerDestroy));
    1083:   }

    1085:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    1086:   PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_converged_reason", &snes->convergedreasonviewer, &snes->convergedreasonformat, NULL));
    1087:   flg = PETSC_FALSE;
    1088:   PetscCall(PetscOptionsBool("-snes_converged_reason_view_cancel", "Remove all converged reason viewers", "SNESConvergedReasonViewCancel", flg, &flg, &set));
    1089:   if (set && flg) PetscCall(SNESConvergedReasonViewCancel(snes));

    1091:   flg = PETSC_FALSE;
    1092:   PetscCall(PetscOptionsBool("-snes_fd", "Use finite differences (slow) to compute Jacobian", "SNESComputeJacobianDefault", flg, &flg, NULL));
    1093:   if (flg) {
    1094:     void *functx;
    1095:     DM    dm;
    1096:     PetscCall(SNESGetDM(snes, &dm));
    1097:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1098:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    1099:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefault, functx));
    1100:     PetscCall(PetscInfo(snes, "Setting default finite difference Jacobian matrix\n"));
    1101:   }

    1103:   flg = PETSC_FALSE;
    1104:   PetscCall(PetscOptionsBool("-snes_fd_function", "Use finite differences (slow) to compute function from user objective", "SNESObjectiveComputeFunctionDefaultFD", flg, &flg, NULL));
    1105:   if (flg) PetscCall(SNESSetFunction(snes, NULL, SNESObjectiveComputeFunctionDefaultFD, NULL));

    1107:   flg = PETSC_FALSE;
    1108:   PetscCall(PetscOptionsBool("-snes_fd_color", "Use finite differences with coloring to compute Jacobian", "SNESComputeJacobianDefaultColor", flg, &flg, NULL));
    1109:   if (flg) {
    1110:     DM dm;
    1111:     PetscCall(SNESGetDM(snes, &dm));
    1112:     PetscCall(DMSNESUnsetJacobianContext_Internal(dm));
    1113:     PetscCall(SNESSetJacobian(snes, snes->jacobian, snes->jacobian_pre, SNESComputeJacobianDefaultColor, NULL));
    1114:     PetscCall(PetscInfo(snes, "Setting default finite difference coloring Jacobian matrix\n"));
    1115:   }

    1117:   flg = PETSC_FALSE;
    1118:   PetscCall(PetscOptionsBool("-snes_mf_operator", "Use a Matrix-Free Jacobian with user-provided matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf_operator, &flg));
    1119:   if (flg && snes->mf_operator) {
    1120:     snes->mf_operator = PETSC_TRUE;
    1121:     snes->mf          = PETSC_TRUE;
    1122:   }
    1123:   flg = PETSC_FALSE;
    1124:   PetscCall(PetscOptionsBool("-snes_mf", "Use a Matrix-Free Jacobian with no matrix for computing the preconditioner", "SNESSetUseMatrixFree", PETSC_FALSE, &snes->mf, &flg));
    1125:   if (!flg && snes->mf_operator) snes->mf = PETSC_TRUE;
    1126:   PetscCall(PetscOptionsInt("-snes_mf_version", "Matrix-Free routines version 1 or 2", "None", snes->mf_version, &snes->mf_version, NULL));

    1128:   PetscCall(PetscOptionsName("-snes_test_function", "Compare hand-coded and finite difference functions", "None", &snes->testFunc));
    1129:   PetscCall(PetscOptionsName("-snes_test_jacobian", "Compare hand-coded and finite difference Jacobians", "None", &snes->testJac));

    1131:   flg = PETSC_FALSE;
    1132:   PetscCall(SNESGetNPCSide(snes, &pcside));
    1133:   PetscCall(PetscOptionsEnum("-snes_npc_side", "SNES nonlinear preconditioner side", "SNESSetNPCSide", PCSides, (PetscEnum)pcside, (PetscEnum *)&pcside, &flg));
    1134:   if (flg) PetscCall(SNESSetNPCSide(snes, pcside));

    1136: #if defined(PETSC_HAVE_SAWS)
    1137:   /*
    1138:     Publish convergence information using SAWs
    1139:   */
    1140:   flg = PETSC_FALSE;
    1141:   PetscCall(PetscOptionsBool("-snes_monitor_saws", "Publish SNES progress using SAWs", "SNESMonitorSet", flg, &flg, NULL));
    1142:   if (flg) {
    1143:     PetscCtx ctx;
    1144:     PetscCall(SNESMonitorSAWsCreate(snes, &ctx));
    1145:     PetscCall(SNESMonitorSet(snes, SNESMonitorSAWs, ctx, SNESMonitorSAWsDestroy));
    1146:   }
    1147: #endif
    1148: #if defined(PETSC_HAVE_SAWS)
    1149:   {
    1150:     PetscBool set;
    1151:     flg = PETSC_FALSE;
    1152:     PetscCall(PetscOptionsBool("-snes_saws_block", "Block for SAWs at end of SNESSolve", "PetscObjectSAWsBlock", ((PetscObject)snes)->amspublishblock, &flg, &set));
    1153:     if (set) PetscCall(PetscObjectSAWsSetBlock((PetscObject)snes, flg));
    1154:   }
    1155: #endif

    1157:   for (i = 0; i < numberofsetfromoptions; i++) PetscCall((*othersetfromoptions[i])(snes));

    1159:   PetscTryTypeMethod(snes, setfromoptions, PetscOptionsObject);

    1161:   /* process any options handlers added with PetscObjectAddOptionsHandler() */
    1162:   PetscCall(PetscObjectProcessOptionsHandlers((PetscObject)snes, PetscOptionsObject));
    1163:   PetscOptionsEnd();

    1165:   if (snes->linesearch) {
    1166:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    1167:     PetscCall(SNESLineSearchSetFromOptions(snes->linesearch));
    1168:   }

    1170:   if (snes->usesksp) {
    1171:     if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    1172:     PetscCall(KSPSetOperators(snes->ksp, snes->jacobian, snes->jacobian_pre));
    1173:     PetscCall(KSPSetFromOptions(snes->ksp));
    1174:   }

    1176:   /* if user has set the SNES NPC type via options database, create it. */
    1177:   PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    1178:   PetscCall(PetscOptionsHasName(((PetscObject)snes)->options, optionsprefix, "-npc_snes_type", &pcset));
    1179:   if (pcset && (!snes->npc)) PetscCall(SNESGetNPC(snes, &snes->npc));
    1180:   if (snes->npc) PetscCall(SNESSetFromOptions(snes->npc));
    1181:   snes->setfromoptionscalled++;
    1182:   PetscFunctionReturn(PETSC_SUCCESS);
    1183: }

    1185: /*@
    1186:   SNESResetFromOptions - Sets various `SNES` and `KSP` parameters from user options ONLY if the `SNESSetFromOptions()` was previously called

    1188:   Collective

    1190:   Input Parameter:
    1191: . snes - the `SNES` context

    1193:   Level: advanced

    1195: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESSetOptionsPrefix()`
    1196: @*/
    1197: PetscErrorCode SNESResetFromOptions(SNES snes)
    1198: {
    1199:   PetscFunctionBegin;
    1200:   if (snes->setfromoptionscalled) PetscCall(SNESSetFromOptions(snes));
    1201:   PetscFunctionReturn(PETSC_SUCCESS);
    1202: }

    1204: /*@C
    1205:   SNESSetComputeApplicationContext - Sets an optional function to compute a user-defined context for
    1206:   the nonlinear solvers.

    1208:   Logically Collective; No Fortran Support

    1210:   Input Parameters:
    1211: + snes    - the `SNES` context
    1212: . compute - function to compute the context
    1213: - destroy - function to destroy the context, see `PetscCtxDestroyFn` for the calling sequence

    1215:   Calling sequence of `compute`:
    1216: + snes - the `SNES` context
    1217: - ctx  - context to be computed

    1219:   Level: intermediate

    1221:   Note:
    1222:   This routine is useful if you are performing grid sequencing or using `SNESFAS` and need the appropriate context generated for each level.

    1224:   Use `SNESSetApplicationContext()` to see the context immediately

    1226: .seealso: [](ch_snes), `SNESGetApplicationContext()`, `SNESSetApplicationContext()`, `PetscCtxDestroyFn`
    1227: @*/
    1228: PetscErrorCode SNESSetComputeApplicationContext(SNES snes, PetscErrorCode (*compute)(SNES snes, PetscCtxRt ctx), PetscCtxDestroyFn *destroy)
    1229: {
    1230:   PetscFunctionBegin;
    1232:   snes->ops->ctxcompute = compute;
    1233:   snes->ops->ctxdestroy = destroy;
    1234:   PetscFunctionReturn(PETSC_SUCCESS);
    1235: }

    1237: /*@
    1238:   SNESSetApplicationContext - Sets the optional user-defined context for the nonlinear solvers.

    1240:   Logically Collective

    1242:   Input Parameters:
    1243: + snes - the `SNES` context
    1244: - ctx  - the user context

    1246:   Level: intermediate

    1248:   Notes:
    1249:   Users can provide a context when constructing the `SNES` options and then access it inside their function, Jacobian computation, or other evaluation function
    1250:   with `SNESGetApplicationContext()`

    1252:   To provide a function that computes the context for you use `SNESSetComputeApplicationContext()`

    1254:   Fortran Note:
    1255:   This only works when `ctx` is a Fortran derived type (it cannot be a `PetscObject`), we recommend writing a Fortran interface definition for this
    1256:   function that tells the Fortran compiler the derived data type that is passed in as the `ctx` argument. See `SNESGetApplicationContext()` for
    1257:   an example.

    1259: .seealso: [](ch_snes), `SNES`, `SNESSetComputeApplicationContext()`, `SNESGetApplicationContext()`
    1260: @*/
    1261: PetscErrorCode SNESSetApplicationContext(SNES snes, PetscCtx ctx)
    1262: {
    1263:   KSP ksp;

    1265:   PetscFunctionBegin;
    1267:   PetscCall(SNESGetKSP(snes, &ksp));
    1268:   PetscCall(KSPSetApplicationContext(ksp, ctx));
    1269:   snes->ctx = ctx;
    1270:   PetscFunctionReturn(PETSC_SUCCESS);
    1271: }

    1273: /*@
    1274:   SNESGetApplicationContext - Gets the user-defined context for the
    1275:   nonlinear solvers set with `SNESGetApplicationContext()` or `SNESSetComputeApplicationContext()`

    1277:   Not Collective

    1279:   Input Parameter:
    1280: . snes - `SNES` context

    1282:   Output Parameter:
    1283: . ctx - the application context

    1285:   Level: intermediate

    1287:   Fortran Notes:
    1288:   This only works when the context is a Fortran derived type or a `PetscObject`. Declare `ctx` with
    1289: .vb
    1290:   type(tUsertype), pointer :: ctx
    1291: .ve

    1293: .seealso: [](ch_snes), `SNESSetApplicationContext()`, `SNESSetComputeApplicationContext()`
    1294: @*/
    1295: PetscErrorCode SNESGetApplicationContext(SNES snes, PetscCtxRt ctx)
    1296: {
    1297:   PetscFunctionBegin;
    1299:   *(void **)ctx = snes->ctx;
    1300:   PetscFunctionReturn(PETSC_SUCCESS);
    1301: }

    1303: /*@
    1304:   SNESSetUseMatrixFree - indicates that `SNES` should use matrix-free finite difference matrix-vector products to apply the Jacobian.

    1306:   Logically Collective

    1308:   Input Parameters:
    1309: + snes        - `SNES` context
    1310: . mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1311: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored. With
    1312:                 this option no matrix-element based preconditioners can be used in the linear solve since the matrix won't be explicitly available

    1314:   Options Database Keys:
    1315: + -snes_mf_operator - use matrix-free only for the mat operator
    1316: . -snes_mf          - use matrix-free for both the mat and pmat operator
    1317: . -snes_fd_color    - compute the Jacobian via coloring and finite differences.
    1318: - -snes_fd          - compute the Jacobian via finite differences (slow)

    1320:   Level: intermediate

    1322:   Note:
    1323:   `SNES` supports three approaches for computing (approximate) Jacobians: user provided via `SNESSetJacobian()`, matrix-free using `MatCreateSNESMF()`,
    1324:   and computing explicitly with
    1325:   finite differences and coloring using `MatFDColoring`. It is also possible to use automatic differentiation and the `MatFDColoring` object.

    1327: .seealso: [](ch_snes), `SNES`, `SNESGetUseMatrixFree()`, `MatCreateSNESMF()`, `SNESComputeJacobianDefaultColor()`, `MatFDColoring`
    1328: @*/
    1329: PetscErrorCode SNESSetUseMatrixFree(SNES snes, PetscBool mf_operator, PetscBool mf)
    1330: {
    1331:   PetscFunctionBegin;
    1335:   snes->mf          = mf_operator ? PETSC_TRUE : mf;
    1336:   snes->mf_operator = mf_operator;
    1337:   PetscFunctionReturn(PETSC_SUCCESS);
    1338: }

    1340: /*@
    1341:   SNESGetUseMatrixFree - indicates if the `SNES` uses matrix-free finite difference matrix vector products to apply the Jacobian.

    1343:   Not Collective, but the resulting flags will be the same on all MPI processes

    1345:   Input Parameter:
    1346: . snes - `SNES` context

    1348:   Output Parameters:
    1349: + mf_operator - use matrix-free only for the Amat used by `SNESSetJacobian()`, this means the user provided Pmat will continue to be used
    1350: - mf          - use matrix-free for both the Amat and Pmat used by `SNESSetJacobian()`, both the Amat and Pmat set in `SNESSetJacobian()` will be ignored

    1352:   Level: intermediate

    1354: .seealso: [](ch_snes), `SNES`, `SNESSetUseMatrixFree()`, `MatCreateSNESMF()`
    1355: @*/
    1356: PetscErrorCode SNESGetUseMatrixFree(SNES snes, PetscBool *mf_operator, PetscBool *mf)
    1357: {
    1358:   PetscFunctionBegin;
    1360:   if (mf) *mf = snes->mf;
    1361:   if (mf_operator) *mf_operator = snes->mf_operator;
    1362:   PetscFunctionReturn(PETSC_SUCCESS);
    1363: }

    1365: /*@
    1366:   SNESGetIterationNumber - Gets the number of nonlinear iterations completed in the current or most recent `SNESSolve()`

    1368:   Not Collective

    1370:   Input Parameter:
    1371: . snes - `SNES` context

    1373:   Output Parameter:
    1374: . iter - iteration number

    1376:   Level: intermediate

    1378:   Notes:
    1379:   For example, during the computation of iteration 2 this would return 1.

    1381:   This is useful for using lagged Jacobians (where one does not recompute the
    1382:   Jacobian at each `SNES` iteration). For example, the code
    1383: .vb
    1384:       ierr = SNESGetIterationNumber(snes,&it);
    1385:       if (!(it % 2)) {
    1386:         [compute Jacobian here]
    1387:       }
    1388: .ve
    1389:   can be used in your function that computes the Jacobian to cause the Jacobian to be
    1390:   recomputed every second `SNES` iteration. See also `SNESSetLagJacobian()`

    1392:   After the `SNES` solve is complete this will return the number of nonlinear iterations used.

    1394: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetLagJacobian()`, `SNESGetLinearSolveIterations()`, `SNESSetMonitor()`
    1395: @*/
    1396: PetscErrorCode SNESGetIterationNumber(SNES snes, PetscInt *iter)
    1397: {
    1398:   PetscFunctionBegin;
    1400:   PetscAssertPointer(iter, 2);
    1401:   *iter = snes->iter;
    1402:   PetscFunctionReturn(PETSC_SUCCESS);
    1403: }

    1405: /*@
    1406:   SNESSetIterationNumber - Sets the current iteration number.

    1408:   Not Collective

    1410:   Input Parameters:
    1411: + snes - `SNES` context
    1412: - iter - iteration number

    1414:   Level: developer

    1416:   Note:
    1417:   This should only be called inside a `SNES` nonlinear solver.

    1419: .seealso: [](ch_snes), `SNESGetLinearSolveIterations()`
    1420: @*/
    1421: PetscErrorCode SNESSetIterationNumber(SNES snes, PetscInt iter)
    1422: {
    1423:   PetscFunctionBegin;
    1425:   PetscCall(PetscObjectSAWsTakeAccess((PetscObject)snes));
    1426:   snes->iter = iter;
    1427:   PetscCall(PetscObjectSAWsGrantAccess((PetscObject)snes));
    1428:   PetscFunctionReturn(PETSC_SUCCESS);
    1429: }

    1431: /*@
    1432:   SNESGetNonlinearStepFailures - Gets the number of unsuccessful steps
    1433:   taken by the nonlinear solver in the current or most recent `SNESSolve()` .

    1435:   Not Collective

    1437:   Input Parameter:
    1438: . snes - `SNES` context

    1440:   Output Parameter:
    1441: . nfails - number of unsuccessful steps attempted

    1443:   Level: intermediate

    1445:   Notes:
    1446:   A failed step is a step that was generated and taken but did not satisfy the requested step criteria. For example,
    1447:   the `SNESLineSearchApply()` could not generate a sufficient decrease in the function norm (in fact it may have produced an increase).

    1449:   Taken steps that produce a infinity or NaN in the function evaluation or generate a `SNESSetFunctionDomainError()`
    1450:   will always immediately terminate the `SNESSolve()` regardless of the value of `maxFails`.

    1452:   `SNESSetMaxNonlinearStepFailures()` determines how many unsuccessful steps are allowed before the `SNESSolve()` terminates

    1454:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1456: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1457:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetMaxNonlinearStepFailures()`
    1458: @*/
    1459: PetscErrorCode SNESGetNonlinearStepFailures(SNES snes, PetscInt *nfails)
    1460: {
    1461:   PetscFunctionBegin;
    1463:   PetscAssertPointer(nfails, 2);
    1464:   *nfails = snes->numFailures;
    1465:   PetscFunctionReturn(PETSC_SUCCESS);
    1466: }

    1468: /*@
    1469:   SNESSetMaxNonlinearStepFailures - Sets the maximum number of unsuccessful steps
    1470:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1472:   Not Collective

    1474:   Input Parameters:
    1475: + snes     - `SNES` context
    1476: - maxFails - maximum of unsuccessful steps allowed, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1478:   Options Database Key:
    1479: . -snes_max_fail n - maximum number of unsuccessful steps allowed

    1481:   Level: intermediate

    1483:   Note:
    1484:   A failed step is a step that was generated and taken but did not satisfy the requested criteria. For example,
    1485:   the `SNESLineSearchApply()` could not generate a sufficient decrease in the function norm (in fact it may have produced an increase).

    1487:   Taken steps that produce a infinity or NaN in the function evaluation or generate a `SNESSetFunctionDomainError()`
    1488:   will always immediately terminate the `SNESSolve()` regardless of the value of `maxFails`.

    1490:   Developer Note:
    1491:   The options database key is wrong for this function name

    1493: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`,
    1494:           `SNESGetLinearSolveFailures()`, `SNESGetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`, `SNESCheckLineSearchFailure()`
    1495: @*/
    1496: PetscErrorCode SNESSetMaxNonlinearStepFailures(SNES snes, PetscInt maxFails)
    1497: {
    1498:   PetscFunctionBegin;

    1501:   if (maxFails == PETSC_UNLIMITED) {
    1502:     snes->maxFailures = PETSC_INT_MAX;
    1503:   } else {
    1504:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1505:     snes->maxFailures = maxFails;
    1506:   }
    1507:   PetscFunctionReturn(PETSC_SUCCESS);
    1508: }

    1510: /*@
    1511:   SNESGetMaxNonlinearStepFailures - Gets the maximum number of unsuccessful steps
    1512:   attempted by the nonlinear solver before it gives up and returns unconverged or generates an error

    1514:   Not Collective

    1516:   Input Parameter:
    1517: . snes - `SNES` context

    1519:   Output Parameter:
    1520: . maxFails - maximum of unsuccessful steps

    1522:   Level: intermediate

    1524: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`,
    1525:           `SNESSetMaxNonlinearStepFailures()`, `SNESGetNonlinearStepFailures()`
    1526: @*/
    1527: PetscErrorCode SNESGetMaxNonlinearStepFailures(SNES snes, PetscInt *maxFails)
    1528: {
    1529:   PetscFunctionBegin;
    1531:   PetscAssertPointer(maxFails, 2);
    1532:   *maxFails = snes->maxFailures;
    1533:   PetscFunctionReturn(PETSC_SUCCESS);
    1534: }

    1536: /*@
    1537:   SNESGetNumberFunctionEvals - Gets the number of user provided function evaluations
    1538:   done by the `SNES` object in the current or most recent `SNESSolve()`

    1540:   Not Collective

    1542:   Input Parameter:
    1543: . snes - `SNES` context

    1545:   Output Parameter:
    1546: . nfuncs - number of evaluations

    1548:   Level: intermediate

    1550:   Note:
    1551:   Reset every time `SNESSolve()` is called unless `SNESSetCountersReset()` is used.

    1553: .seealso: [](ch_snes), `SNES`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`, `SNESGetLinearSolveFailures()`, `SNESSetCountersReset()`
    1554: @*/
    1555: PetscErrorCode SNESGetNumberFunctionEvals(SNES snes, PetscInt *nfuncs)
    1556: {
    1557:   PetscFunctionBegin;
    1559:   PetscAssertPointer(nfuncs, 2);
    1560:   *nfuncs = snes->nfuncs;
    1561:   PetscFunctionReturn(PETSC_SUCCESS);
    1562: }

    1564: /*@
    1565:   SNESGetLinearSolveFailures - Gets the number of failed (non-converged)
    1566:   linear solvers in the current or most recent `SNESSolve()`

    1568:   Not Collective

    1570:   Input Parameter:
    1571: . snes - `SNES` context

    1573:   Output Parameter:
    1574: . nfails - number of failed solves

    1576:   Options Database Key:
    1577: . -snes_max_linear_solve_fail num - The number of failures before the solve is terminated

    1579:   Level: intermediate

    1581:   Note:
    1582:   This counter is reset to zero for each successive call to `SNESSolve()`.

    1584: .seealso: [](ch_snes), `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1585: @*/
    1586: PetscErrorCode SNESGetLinearSolveFailures(SNES snes, PetscInt *nfails)
    1587: {
    1588:   PetscFunctionBegin;
    1590:   PetscAssertPointer(nfails, 2);
    1591:   *nfails = snes->numLinearSolveFailures;
    1592:   PetscFunctionReturn(PETSC_SUCCESS);
    1593: }

    1595: /*@
    1596:   SNESSetMaxLinearSolveFailures - the number of failed linear solve attempts
    1597:   allowed before `SNES` returns with a diverged reason of `SNES_DIVERGED_LINEAR_SOLVE`

    1599:   Logically Collective

    1601:   Input Parameters:
    1602: + snes     - `SNES` context
    1603: - maxFails - maximum allowed linear solve failures, use `PETSC_UNLIMITED` to have no limit on the number of failures

    1605:   Options Database Key:
    1606: . -snes_max_linear_solve_fail num - The number of failures before the solve is terminated

    1608:   Level: intermediate

    1610:   Note:
    1611:   By default this is 0; that is `SNES` returns on the first failed linear solve

    1613:   Developer Note:
    1614:   The options database key is wrong for this function name

    1616: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESGetLinearSolveIterations()`
    1617: @*/
    1618: PetscErrorCode SNESSetMaxLinearSolveFailures(SNES snes, PetscInt maxFails)
    1619: {
    1620:   PetscFunctionBegin;

    1624:   if (maxFails == PETSC_UNLIMITED) {
    1625:     snes->maxLinearSolveFailures = PETSC_INT_MAX;
    1626:   } else {
    1627:     PetscCheck(maxFails >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Cannot have a negative maximum number of failures");
    1628:     snes->maxLinearSolveFailures = maxFails;
    1629:   }
    1630:   PetscFunctionReturn(PETSC_SUCCESS);
    1631: }

    1633: /*@
    1634:   SNESGetMaxLinearSolveFailures - gets the maximum number of linear solve failures that
    1635:   are allowed before `SNES` returns as unsuccessful

    1637:   Not Collective

    1639:   Input Parameter:
    1640: . snes - `SNES` context

    1642:   Output Parameter:
    1643: . maxFails - maximum of unsuccessful solves allowed

    1645:   Level: intermediate

    1647:   Note:
    1648:   By default this is 1; that is `SNES` returns on the first failed linear solve

    1650: .seealso: [](ch_snes), `SNESSetErrorIfNotConverged()`, `SNESGetLinearSolveFailures()`, `SNESGetLinearSolveIterations()`, `SNESSetMaxLinearSolveFailures()`
    1651: @*/
    1652: PetscErrorCode SNESGetMaxLinearSolveFailures(SNES snes, PetscInt *maxFails)
    1653: {
    1654:   PetscFunctionBegin;
    1656:   PetscAssertPointer(maxFails, 2);
    1657:   *maxFails = snes->maxLinearSolveFailures;
    1658:   PetscFunctionReturn(PETSC_SUCCESS);
    1659: }

    1661: /*@
    1662:   SNESGetLinearSolveIterations - Gets the total number of linear iterations
    1663:   used by the nonlinear solver in the most recent `SNESSolve()`

    1665:   Not Collective

    1667:   Input Parameter:
    1668: . snes - `SNES` context

    1670:   Output Parameter:
    1671: . lits - number of linear iterations

    1673:   Level: intermediate

    1675:   Notes:
    1676:   This counter is reset to zero for each successive call to `SNESSolve()` unless `SNESSetCountersReset()` is used.

    1678:   If the linear solver fails inside the `SNESSolve()` the iterations for that call to the linear solver are not included. If you wish to count them
    1679:   then call `KSPGetIterationNumber()` after the failed solve.

    1681: .seealso: [](ch_snes), `SNES`, `SNESGetIterationNumber()`, `SNESGetLinearSolveFailures()`, `SNESGetMaxLinearSolveFailures()`, `SNESSetCountersReset()`
    1682: @*/
    1683: PetscErrorCode SNESGetLinearSolveIterations(SNES snes, PetscInt *lits)
    1684: {
    1685:   PetscFunctionBegin;
    1687:   PetscAssertPointer(lits, 2);
    1688:   *lits = snes->linear_its;
    1689:   PetscFunctionReturn(PETSC_SUCCESS);
    1690: }

    1692: /*@
    1693:   SNESSetCountersReset - Sets whether or not the counters for linear iterations and function evaluations
    1694:   are reset every time `SNESSolve()` is called.

    1696:   Logically Collective

    1698:   Input Parameters:
    1699: + snes  - `SNES` context
    1700: - reset - whether to reset the counters or not, defaults to `PETSC_TRUE`

    1702:   Level: developer

    1704: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1705: @*/
    1706: PetscErrorCode SNESSetCountersReset(SNES snes, PetscBool reset)
    1707: {
    1708:   PetscFunctionBegin;
    1711:   snes->counters_reset = reset;
    1712:   PetscFunctionReturn(PETSC_SUCCESS);
    1713: }

    1715: /*@
    1716:   SNESResetCounters - Reset counters for linear iterations and function evaluations.

    1718:   Logically Collective

    1720:   Input Parameters:
    1721: . snes - `SNES` context

    1723:   Level: developer

    1725:   Note:
    1726:   It honors the flag set with `SNESSetCountersReset()`

    1728: .seealso: [](ch_snes), `SNESGetNumberFunctionEvals()`, `SNESGetLinearSolveIterations()`, `SNESGetNPC()`
    1729: @*/
    1730: PetscErrorCode SNESResetCounters(SNES snes)
    1731: {
    1732:   PetscFunctionBegin;
    1734:   if (snes->counters_reset) {
    1735:     snes->nfuncs      = 0;
    1736:     snes->linear_its  = 0;
    1737:     snes->numFailures = 0;
    1738:   }
    1739:   PetscFunctionReturn(PETSC_SUCCESS);
    1740: }

    1742: /*@
    1743:   SNESSetKSP - Sets a `KSP` context for the `SNES` object to use

    1745:   Not Collective, but the `SNES` and `KSP` objects must live on the same `MPI_Comm`

    1747:   Input Parameters:
    1748: + snes - the `SNES` context
    1749: - ksp  - the `KSP` context

    1751:   Level: developer

    1753:   Notes:
    1754:   The `SNES` object already has its `KSP` object, you can obtain with `SNESGetKSP()`
    1755:   so this routine is rarely needed.

    1757:   The `KSP` object that is already in the `SNES` object has its reference count
    1758:   decreased by one when this is called.

    1760: .seealso: [](ch_snes), `SNES`, `KSP`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`
    1761: @*/
    1762: PetscErrorCode SNESSetKSP(SNES snes, KSP ksp)
    1763: {
    1764:   PetscFunctionBegin;
    1767:   PetscCheckSameComm(snes, 1, ksp, 2);
    1768:   PetscCall(PetscObjectReference((PetscObject)ksp));
    1769:   PetscCall(PetscObjectDereference((PetscObject)snes->ksp));
    1770:   snes->ksp = ksp;
    1771:   PetscFunctionReturn(PETSC_SUCCESS);
    1772: }

    1774: /*@
    1775:   SNESParametersInitialize - Sets all the parameters in `snes` to their default value (when `SNESCreate()` was called) if they
    1776:   currently contain default values

    1778:   Collective

    1780:   Input Parameter:
    1781: . snes - the `SNES` object

    1783:   Level: developer

    1785:   Developer Note:
    1786:   This is called by all the `SNESCreate_XXX()` routines.

    1788: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    1789:           `PetscObjectParameterSetDefault()`
    1790: @*/
    1791: PetscErrorCode SNESParametersInitialize(SNES snes)
    1792: {
    1793:   PetscObjectParameterSetDefault(snes, max_its, 50);
    1794:   PetscObjectParameterSetDefault(snes, max_funcs, 10000);
    1795:   PetscObjectParameterSetDefault(snes, rtol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1796:   PetscObjectParameterSetDefault(snes, abstol, PetscDefined(USE_REAL_SINGLE) ? 1.e-25 : 1.e-50);
    1797:   PetscObjectParameterSetDefault(snes, stol, PetscDefined(USE_REAL_SINGLE) ? 1.e-5 : 1.e-8);
    1798:   PetscObjectParameterSetDefault(snes, divtol, 1.e4);
    1799:   return PETSC_SUCCESS;
    1800: }

    1802: /*@
    1803:   SNESCreate - Creates a nonlinear solver context used to manage a set of nonlinear solves

    1805:   Collective

    1807:   Input Parameter:
    1808: . comm - MPI communicator

    1810:   Output Parameter:
    1811: . outsnes - the new `SNES` context

    1813:   Options Database Keys:
    1814: + -snes_mf          - Activates default matrix-free Jacobian-vector products, and no matrix to construct a preconditioner
    1815: . -snes_mf_operator - Activates default matrix-free Jacobian-vector products, and a user-provided matrix as set by `SNESSetJacobian()`
    1816: . -snes_fd_coloring - uses a relative fast computation of the Jacobian using finite differences and a graph coloring
    1817: - -snes_fd          - Uses (slow!) finite differences to compute Jacobian

    1819:   Level: beginner

    1821:   Developer Notes:
    1822:   `SNES` always creates a `KSP` object even though many `SNES` methods do not use it. This is
    1823:   unfortunate and should be fixed at some point. The flag snes->usesksp indicates if the
    1824:   particular method does use `KSP` and regulates if the information about the `KSP` is printed
    1825:   in `SNESView()`.

    1827:   `TSSetFromOptions()` does call `SNESSetFromOptions()` which can lead to users being confused
    1828:   by help messages about meaningless `SNES` options.

    1830:   `SNES` always creates the `snes->kspconvctx` even though it is used by only one type. This should be fixed.

    1832: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESDestroy()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`
    1833: @*/
    1834: PetscErrorCode SNESCreate(MPI_Comm comm, SNES *outsnes)
    1835: {
    1836:   SNES       snes;
    1837:   SNESKSPEW *kctx;

    1839:   PetscFunctionBegin;
    1840:   PetscAssertPointer(outsnes, 2);
    1841:   PetscCall(SNESInitializePackage());

    1843:   PetscCall(PetscHeaderCreate(snes, SNES_CLASSID, "SNES", "Nonlinear solver", "SNES", comm, SNESDestroy, SNESView));
    1844:   snes->ops->converged = SNESConvergedDefault;
    1845:   snes->usesksp        = PETSC_TRUE;
    1846:   snes->norm           = 0.0;
    1847:   snes->xnorm          = 0.0;
    1848:   snes->ynorm          = 0.0;
    1849:   snes->normschedule   = SNES_NORM_ALWAYS;
    1850:   snes->functype       = SNES_FUNCTION_DEFAULT;
    1851:   snes->ttol           = 0.0;

    1853:   snes->rnorm0               = 0;
    1854:   snes->nfuncs               = 0;
    1855:   snes->numFailures          = 0;
    1856:   snes->maxFailures          = 1;
    1857:   snes->linear_its           = 0;
    1858:   snes->lagjacobian          = 1;
    1859:   snes->jac_iter             = 0;
    1860:   snes->lagjac_persist       = PETSC_FALSE;
    1861:   snes->lagpreconditioner    = 1;
    1862:   snes->pre_iter             = 0;
    1863:   snes->lagpre_persist       = PETSC_FALSE;
    1864:   snes->numbermonitors       = 0;
    1865:   snes->numberreasonviews    = 0;
    1866:   snes->data                 = NULL;
    1867:   snes->setupcalled          = PETSC_FALSE;
    1868:   snes->ksp_ewconv           = PETSC_FALSE;
    1869:   snes->nwork                = 0;
    1870:   snes->work                 = NULL;
    1871:   snes->nvwork               = 0;
    1872:   snes->vwork                = NULL;
    1873:   snes->conv_hist_len        = 0;
    1874:   snes->conv_hist_max        = 0;
    1875:   snes->conv_hist            = NULL;
    1876:   snes->conv_hist_its        = NULL;
    1877:   snes->conv_hist_reset      = PETSC_TRUE;
    1878:   snes->counters_reset       = PETSC_TRUE;
    1879:   snes->vec_func_init_set    = PETSC_FALSE;
    1880:   snes->reason               = SNES_CONVERGED_ITERATING;
    1881:   snes->npcside              = PC_RIGHT;
    1882:   snes->setfromoptionscalled = 0;

    1884:   snes->mf          = PETSC_FALSE;
    1885:   snes->mf_operator = PETSC_FALSE;
    1886:   snes->mf_version  = 1;

    1888:   snes->numLinearSolveFailures = 0;
    1889:   snes->maxLinearSolveFailures = 1;

    1891:   snes->vizerotolerance     = 1.e-8;
    1892:   snes->checkjacdomainerror = PetscDefined(USE_DEBUG) ? PETSC_TRUE : PETSC_FALSE;

    1894:   /* Set this to true if the implementation of SNESSolve_XXX does compute the residual at the final solution. */
    1895:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    1897:   /* Create context to compute Eisenstat-Walker relative tolerance for KSP */
    1898:   PetscCall(PetscNew(&kctx));

    1900:   snes->kspconvctx  = kctx;
    1901:   kctx->version     = 2;
    1902:   kctx->rtol_0      = 0.3; /* Eisenstat and Walker suggest rtol_0=.5, but
    1903:                              this was too large for some test cases */
    1904:   kctx->rtol_last   = 0.0;
    1905:   kctx->rtol_max    = 0.9;
    1906:   kctx->gamma       = 1.0;
    1907:   kctx->alpha       = 0.5 * (1.0 + PetscSqrtReal(5.0));
    1908:   kctx->alpha2      = kctx->alpha;
    1909:   kctx->threshold   = 0.1;
    1910:   kctx->lresid_last = 0.0;
    1911:   kctx->norm_last   = 0.0;

    1913:   kctx->rk_last     = 0.0;
    1914:   kctx->rk_last_2   = 0.0;
    1915:   kctx->rtol_last_2 = 0.0;
    1916:   kctx->v4_p1       = 0.1;
    1917:   kctx->v4_p2       = 0.4;
    1918:   kctx->v4_p3       = 0.7;
    1919:   kctx->v4_m1       = 0.8;
    1920:   kctx->v4_m2       = 0.5;
    1921:   kctx->v4_m3       = 0.1;
    1922:   kctx->v4_m4       = 0.5;

    1924:   PetscCall(SNESParametersInitialize(snes));
    1925:   *outsnes = snes;
    1926:   PetscFunctionReturn(PETSC_SUCCESS);
    1927: }

    1929: /*@C
    1930:   SNESSetFunction - Sets the function evaluation routine and function
    1931:   vector for use by the `SNES` routines in solving systems of nonlinear
    1932:   equations.

    1934:   Logically Collective

    1936:   Input Parameters:
    1937: + snes - the `SNES` context
    1938: . r    - vector to store function values, may be `NULL`
    1939: . f    - function evaluation routine;  for calling sequence see `SNESFunctionFn`
    1940: - ctx  - [optional] user-defined context for private data for the
    1941:          function evaluation routine (may be `NULL`)

    1943:   Level: beginner

    1945: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetPicard()`, `SNESFunctionFn`
    1946: @*/
    1947: PetscErrorCode SNESSetFunction(SNES snes, Vec r, SNESFunctionFn *f, PetscCtx ctx)
    1948: {
    1949:   DM dm;

    1951:   PetscFunctionBegin;
    1953:   if (r) {
    1955:     PetscCheckSameComm(snes, 1, r, 2);
    1956:     PetscCall(PetscObjectReference((PetscObject)r));
    1957:     PetscCall(VecDestroy(&snes->vec_func));
    1958:     snes->vec_func = r;
    1959:   }
    1960:   PetscCall(SNESGetDM(snes, &dm));
    1961:   PetscCall(DMSNESSetFunction(dm, f, ctx));
    1962:   if (f == SNESPicardComputeFunction) PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    1963:   PetscFunctionReturn(PETSC_SUCCESS);
    1964: }

    1966: /*@C
    1967:   SNESSetInitialFunction - Set an already computed function evaluation at the initial guess to be reused by `SNESSolve()`.

    1969:   Logically Collective

    1971:   Input Parameters:
    1972: + snes - the `SNES` context
    1973: - f    - vector to store function value

    1975:   Level: developer

    1977:   Notes:
    1978:   This should not be modified during the solution procedure.

    1980:   This is used extensively in the `SNESFAS` hierarchy and in nonlinear preconditioning.

    1982: .seealso: [](ch_snes), `SNES`, `SNESFAS`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetInitialFunctionNorm()`
    1983: @*/
    1984: PetscErrorCode SNESSetInitialFunction(SNES snes, Vec f)
    1985: {
    1986:   Vec vec_func;

    1988:   PetscFunctionBegin;
    1991:   PetscCheckSameComm(snes, 1, f, 2);
    1992:   if (snes->npcside == PC_LEFT && snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    1993:     snes->vec_func_init_set = PETSC_FALSE;
    1994:     PetscFunctionReturn(PETSC_SUCCESS);
    1995:   }
    1996:   PetscCall(SNESGetFunction(snes, &vec_func, NULL, NULL));
    1997:   PetscCall(VecCopy(f, vec_func));

    1999:   snes->vec_func_init_set = PETSC_TRUE;
    2000:   PetscFunctionReturn(PETSC_SUCCESS);
    2001: }

    2003: /*@
    2004:   SNESSetNormSchedule - Sets the `SNESNormSchedule` used in convergence and monitoring
    2005:   of the `SNES` method, when norms are computed in the solving process

    2007:   Logically Collective

    2009:   Input Parameters:
    2010: + snes         - the `SNES` context
    2011: - normschedule - the frequency of norm computation

    2013:   Options Database Key:
    2014: . -snes_norm_schedule (none|always|initialonly|finalonly|initialfinalonly) - set the schedule

    2016:   Level: advanced

    2018:   Notes:
    2019:   Only certain `SNES` methods support certain `SNESNormSchedules`.  Most require evaluation
    2020:   of the nonlinear function and the taking of its norm at every iteration to
    2021:   even ensure convergence at all.  However, methods such as custom Gauss-Seidel methods
    2022:   `SNESNGS` and the like do not require the norm of the function to be computed, and therefore
    2023:   may either be monitored for convergence or not.  As these are often used as nonlinear
    2024:   preconditioners, monitoring the norm of their error is not a useful enterprise within
    2025:   their solution.

    2027: .seealso: [](ch_snes), `SNESNormSchedule`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`
    2028: @*/
    2029: PetscErrorCode SNESSetNormSchedule(SNES snes, SNESNormSchedule normschedule)
    2030: {
    2031:   PetscFunctionBegin;
    2033:   snes->normschedule = normschedule;
    2034:   PetscFunctionReturn(PETSC_SUCCESS);
    2035: }

    2037: /*@
    2038:   SNESGetNormSchedule - Gets the `SNESNormSchedule` used in convergence and monitoring
    2039:   of the `SNES` method.

    2041:   Logically Collective

    2043:   Input Parameters:
    2044: + snes         - the `SNES` context
    2045: - normschedule - the type of the norm used

    2047:   Level: advanced

    2049: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2050: @*/
    2051: PetscErrorCode SNESGetNormSchedule(SNES snes, SNESNormSchedule *normschedule)
    2052: {
    2053:   PetscFunctionBegin;
    2055:   *normschedule = snes->normschedule;
    2056:   PetscFunctionReturn(PETSC_SUCCESS);
    2057: }

    2059: /*@
    2060:   SNESSetFunctionNorm - Sets the last computed residual norm.

    2062:   Logically Collective

    2064:   Input Parameters:
    2065: + snes - the `SNES` context
    2066: - norm - the value of the norm

    2068:   Level: developer

    2070: .seealso: [](ch_snes), `SNES`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2071: @*/
    2072: PetscErrorCode SNESSetFunctionNorm(SNES snes, PetscReal norm)
    2073: {
    2074:   PetscFunctionBegin;
    2076:   snes->norm = norm;
    2077:   PetscFunctionReturn(PETSC_SUCCESS);
    2078: }

    2080: /*@
    2081:   SNESGetFunctionNorm - Gets the last computed norm of the residual

    2083:   Not Collective

    2085:   Input Parameter:
    2086: . snes - the `SNES` context

    2088:   Output Parameter:
    2089: . norm - the last computed residual norm

    2091:   Level: developer

    2093: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2094: @*/
    2095: PetscErrorCode SNESGetFunctionNorm(SNES snes, PetscReal *norm)
    2096: {
    2097:   PetscFunctionBegin;
    2099:   PetscAssertPointer(norm, 2);
    2100:   *norm = snes->norm;
    2101:   PetscFunctionReturn(PETSC_SUCCESS);
    2102: }

    2104: /*@
    2105:   SNESGetUpdateNorm - Gets the last computed norm of the solution update

    2107:   Not Collective

    2109:   Input Parameter:
    2110: . snes - the `SNES` context

    2112:   Output Parameter:
    2113: . ynorm - the last computed update norm

    2115:   Level: developer

    2117:   Note:
    2118:   The new solution is the current solution plus the update, so this norm is an indication of the size of the update

    2120: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`
    2121: @*/
    2122: PetscErrorCode SNESGetUpdateNorm(SNES snes, PetscReal *ynorm)
    2123: {
    2124:   PetscFunctionBegin;
    2126:   PetscAssertPointer(ynorm, 2);
    2127:   *ynorm = snes->ynorm;
    2128:   PetscFunctionReturn(PETSC_SUCCESS);
    2129: }

    2131: /*@
    2132:   SNESGetSolutionNorm - Gets the last computed norm of the solution

    2134:   Not Collective

    2136:   Input Parameter:
    2137: . snes - the `SNES` context

    2139:   Output Parameter:
    2140: . xnorm - the last computed solution norm

    2142:   Level: developer

    2144: .seealso: [](ch_snes), `SNES`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `SNESGetFunctionNorm()`, `SNESGetUpdateNorm()`
    2145: @*/
    2146: PetscErrorCode SNESGetSolutionNorm(SNES snes, PetscReal *xnorm)
    2147: {
    2148:   PetscFunctionBegin;
    2150:   PetscAssertPointer(xnorm, 2);
    2151:   *xnorm = snes->xnorm;
    2152:   PetscFunctionReturn(PETSC_SUCCESS);
    2153: }

    2155: /*@
    2156:   SNESSetFunctionType - Sets the `SNESFunctionType`
    2157:   of the `SNES` method.

    2159:   Logically Collective

    2161:   Input Parameters:
    2162: + snes - the `SNES` context
    2163: - type - the function type

    2165:   Level: developer

    2167:   Values of the function type\:
    2168: +  `SNES_FUNCTION_DEFAULT`          - the default for the given `SNESType`
    2169: .  `SNES_FUNCTION_UNPRECONDITIONED` - an unpreconditioned function evaluation (this is the function provided with `SNESSetFunction()`
    2170: -  `SNES_FUNCTION_PRECONDITIONED`   - a transformation of the function provided with `SNESSetFunction()`

    2172:   Note:
    2173:   Different `SNESType`s use this value in different ways

    2175: .seealso: [](ch_snes), `SNES`, `SNESFunctionType`, `SNESGetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2176: @*/
    2177: PetscErrorCode SNESSetFunctionType(SNES snes, SNESFunctionType type)
    2178: {
    2179:   PetscFunctionBegin;
    2181:   snes->functype = type;
    2182:   PetscFunctionReturn(PETSC_SUCCESS);
    2183: }

    2185: /*@
    2186:   SNESGetFunctionType - Gets the `SNESFunctionType` used in convergence and monitoring set with `SNESSetFunctionType()`
    2187:   of the SNES method.

    2189:   Logically Collective

    2191:   Input Parameters:
    2192: + snes - the `SNES` context
    2193: - type - the type of the function evaluation, see `SNESSetFunctionType()`

    2195:   Level: advanced

    2197: .seealso: [](ch_snes), `SNESSetFunctionType()`, `SNESFunctionType`, `SNESSetNormSchedule()`, `SNESComputeFunction()`, `VecNorm()`, `SNESSetFunction()`, `SNESSetInitialFunction()`, `SNESNormSchedule`
    2198: @*/
    2199: PetscErrorCode SNESGetFunctionType(SNES snes, SNESFunctionType *type)
    2200: {
    2201:   PetscFunctionBegin;
    2203:   *type = snes->functype;
    2204:   PetscFunctionReturn(PETSC_SUCCESS);
    2205: }

    2207: /*@C
    2208:   SNESSetNGS - Sets the user nonlinear Gauss-Seidel routine for
    2209:   use with composed nonlinear solvers.

    2211:   Input Parameters:
    2212: + snes - the `SNES` context, usually of the `SNESType` `SNESNGS`
    2213: . f    - function evaluation routine to apply Gauss-Seidel, see `SNESNGSFn` for calling sequence
    2214: - ctx  - [optional] user-defined context for private data for the smoother evaluation routine (may be `NULL`)

    2216:   Level: intermediate

    2218:   Note:
    2219:   The `SNESNGS` routines are used by the composed nonlinear solver to generate
    2220:   a problem appropriate update to the solution, particularly `SNESFAS`.

    2222: .seealso: [](ch_snes), `SNESNGS`, `SNESGetNGS()`, `SNESNCG`, `SNESGetFunction()`, `SNESComputeNGS()`, `SNESNGSFn`
    2223: @*/
    2224: PetscErrorCode SNESSetNGS(SNES snes, SNESNGSFn *f, PetscCtx ctx)
    2225: {
    2226:   DM dm;

    2228:   PetscFunctionBegin;
    2230:   PetscCall(SNESGetDM(snes, &dm));
    2231:   PetscCall(DMSNESSetNGS(dm, f, ctx));
    2232:   PetscFunctionReturn(PETSC_SUCCESS);
    2233: }

    2235: /*
    2236:      This is used for -snes_mf_operator; it uses a duplicate of snes->jacobian_pre because snes->jacobian_pre cannot be
    2237:    changed during the KSPSolve()
    2238: */
    2239: PetscErrorCode SNESPicardComputeMFFunction(SNES snes, Vec x, Vec f, PetscCtx ctx)
    2240: {
    2241:   DM     dm;
    2242:   DMSNES sdm;

    2244:   PetscFunctionBegin;
    2245:   PetscCall(SNESGetDM(snes, &dm));
    2246:   PetscCall(DMGetDMSNES(dm, &sdm));
    2247:   /*  A(x)*x - b(x) */
    2248:   if (sdm->ops->computepfunction) {
    2249:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2250:     PetscCall(VecScale(f, -1.0));
    2251:     /* Cannot share nonzero pattern because of the possible use of SNESComputeJacobianDefault() */
    2252:     if (!snes->picard) PetscCall(MatDuplicate(snes->jacobian_pre, MAT_DO_NOT_COPY_VALUES, &snes->picard));
    2253:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2254:     PetscCall(MatMultAdd(snes->picard, x, f, f));
    2255:   } else {
    2256:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->picard, snes->picard, sdm->pctx));
    2257:     PetscCall(MatMult(snes->picard, x, f));
    2258:   }
    2259:   PetscFunctionReturn(PETSC_SUCCESS);
    2260: }

    2262: PetscErrorCode SNESPicardComputeFunction(SNES snes, Vec x, Vec f, PetscCtx ctx)
    2263: {
    2264:   DM     dm;
    2265:   DMSNES sdm;

    2267:   PetscFunctionBegin;
    2268:   PetscCall(SNESGetDM(snes, &dm));
    2269:   PetscCall(DMGetDMSNES(dm, &sdm));
    2270:   /*  A(x)*x - b(x) */
    2271:   if (sdm->ops->computepfunction) {
    2272:     PetscCallBack("SNES Picard callback function", (*sdm->ops->computepfunction)(snes, x, f, sdm->pctx));
    2273:     PetscCall(VecScale(f, -1.0));
    2274:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2275:     PetscCall(MatMultAdd(snes->jacobian_pre, x, f, f));
    2276:   } else {
    2277:     PetscCallBack("SNES Picard callback Jacobian", (*sdm->ops->computepjacobian)(snes, x, snes->jacobian, snes->jacobian_pre, sdm->pctx));
    2278:     PetscCall(MatMult(snes->jacobian_pre, x, f));
    2279:   }
    2280:   PetscFunctionReturn(PETSC_SUCCESS);
    2281: }

    2283: PetscErrorCode SNESPicardComputeJacobian(SNES snes, Vec x1, Mat J, Mat B, PetscCtx ctx)
    2284: {
    2285:   PetscFunctionBegin;
    2286:   /* the jacobian matrix should be pre-filled in SNESPicardComputeFunction */
    2287:   /* must assembly if matrix-free to get the last SNES solution */
    2288:   PetscCall(MatAssemblyBegin(J, MAT_FINAL_ASSEMBLY));
    2289:   PetscCall(MatAssemblyEnd(J, MAT_FINAL_ASSEMBLY));
    2290:   PetscFunctionReturn(PETSC_SUCCESS);
    2291: }

    2293: /*@C
    2294:   SNESSetPicard - Use `SNES` to solve the system $A(x) x = bp(x) + b $ via a Picard type iteration (Picard linearization)

    2296:   Logically Collective

    2298:   Input Parameters:
    2299: + snes - the `SNES` context
    2300: . r    - vector to store function values, may be `NULL`
    2301: . bp   - function evaluation routine, may be `NULL`, for the calling sequence see `SNESFunctionFn`
    2302: . Amat - matrix with which $A(x) x - bp(x) - b$ is to be computed
    2303: . Pmat - matrix from which preconditioner is computed (usually the same as `Amat`)
    2304: . J    - function to compute matrix values, for the calling sequence see `SNESJacobianFn`
    2305: - ctx  - [optional] user-defined context for private data for the function evaluation routine (may be `NULL`)

    2307:   Level: intermediate

    2309:   Notes:
    2310:   It is often better to provide the nonlinear function $F()$ and some approximation to its Jacobian directly and use
    2311:   an approximate Newton solver. This interface is provided to allow porting/testing a previous Picard based code in PETSc before converting it to approximate Newton.

    2313:   One can call `SNESSetPicard()` or `SNESSetFunction()` (and possibly `SNESSetJacobian()`) but cannot call both

    2315:   Solves the equation $A(x) x = bp(x) - b$ via the defect correction algorithm $A(x^{n}) (x^{n+1} - x^{n}) = bp(x^{n}) + b - A(x^{n})x^{n}$.
    2316:   When an exact solver is used this corresponds to the "classic" Picard $A(x^{n}) x^{n+1} = bp(x^{n}) + b$ iteration.

    2318:   Run with `-snes_mf_operator` to solve the system with Newton's method using $A(x^{n})$ to construct the preconditioner.

    2320:   We implement the defect correction form of the Picard iteration because it converges much more generally when inexact linear solvers are used then
    2321:   the direct Picard iteration $A(x^n) x^{n+1} = bp(x^n) + b$

    2323:   There is some controversity over the definition of a Picard iteration for nonlinear systems but almost everyone agrees that it involves a linear solve and some
    2324:   believe it is the iteration  $A(x^{n}) x^{n+1} = b(x^{n})$ hence we use the name Picard. If anyone has an authoritative  reference that defines the Picard iteration
    2325:   different please contact us at petsc-dev@mcs.anl.gov and we'll have an entirely new argument \:-).

    2327:   When used with `-snes_mf_operator` this will run matrix-free Newton's method where the matrix-vector product is of the true Jacobian of $A(x)x - bp(x) - b$ and
    2328:   $A(x^{n})$ is used to build the preconditioner

    2330:   When used with `-snes_fd` this will compute the true Jacobian (very slowly one column at a time) and thus represent Newton's method.

    2332:   When used with `-snes_fd_coloring` this will compute the Jacobian via coloring and thus represent a faster implementation of Newton's method. But the
    2333:   the nonzero structure of the Jacobian is, in general larger than that of the Picard matrix $A$ so you must provide in $A$ the needed nonzero structure for the correct
    2334:   coloring. When using `DMDA` this may mean creating the matrix $A$ with `DMCreateMatrix()` using a wider stencil than strictly needed for $A$ or with a `DMDA_STENCIL_BOX`.
    2335:   See the comment in src/snes/tutorials/ex15.c.

    2337: .seealso: [](ch_snes), `SNES`, `SNESGetFunction()`, `SNESSetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESGetPicard()`, `SNESLineSearchPreCheckPicard()`,
    2338:           `SNESFunctionFn`, `SNESJacobianFn`
    2339: @*/
    2340: PetscErrorCode SNESSetPicard(SNES snes, Vec r, SNESFunctionFn *bp, Mat Amat, Mat Pmat, SNESJacobianFn *J, PetscCtx ctx)
    2341: {
    2342:   DM dm;

    2344:   PetscFunctionBegin;
    2346:   PetscCall(SNESGetDM(snes, &dm));
    2347:   PetscCall(DMSNESSetPicard(dm, bp, J, ctx));
    2348:   PetscCall(DMSNESSetMFFunction(dm, SNESPicardComputeMFFunction, ctx));
    2349:   PetscCall(SNESSetFunction(snes, r, SNESPicardComputeFunction, ctx));
    2350:   PetscCall(SNESSetJacobian(snes, Amat, Pmat, SNESPicardComputeJacobian, ctx));
    2351:   PetscFunctionReturn(PETSC_SUCCESS);
    2352: }

    2354: /*@C
    2355:   SNESGetPicard - Returns the context for the Picard iteration

    2357:   Not Collective, but `Vec` is parallel if `SNES` is parallel. Collective if `Vec` is requested, but has not been created yet.

    2359:   Input Parameter:
    2360: . snes - the `SNES` context

    2362:   Output Parameters:
    2363: + r    - the function (or `NULL`)
    2364: . f    - the function (or `NULL`);  for calling sequence see `SNESFunctionFn`
    2365: . Amat - the matrix used to defined the operation A(x) x - b(x) (or `NULL`)
    2366: . Pmat - the matrix from which the preconditioner will be constructed (or `NULL`)
    2367: . J    - the function for matrix evaluation (or `NULL`);  for calling sequence see `SNESJacobianFn`
    2368: - ctx  - the function context (or `NULL`)

    2370:   Level: advanced

    2372: .seealso: [](ch_snes), `SNESSetFunction()`, `SNESSetPicard()`, `SNESGetFunction()`, `SNESGetJacobian()`, `SNESGetDM()`, `SNESFunctionFn`, `SNESJacobianFn`
    2373: @*/
    2374: PetscErrorCode SNESGetPicard(SNES snes, Vec *r, SNESFunctionFn **f, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, PetscCtxRt ctx)
    2375: {
    2376:   DM dm;

    2378:   PetscFunctionBegin;
    2380:   PetscCall(SNESGetFunction(snes, r, NULL, NULL));
    2381:   PetscCall(SNESGetJacobian(snes, Amat, Pmat, NULL, NULL));
    2382:   PetscCall(SNESGetDM(snes, &dm));
    2383:   PetscCall(DMSNESGetPicard(dm, f, J, ctx));
    2384:   PetscFunctionReturn(PETSC_SUCCESS);
    2385: }

    2387: /*@C
    2388:   SNESSetComputeInitialGuess - Sets a routine used to compute an initial guess for the nonlinear problem

    2390:   Logically Collective

    2392:   Input Parameters:
    2393: + snes - the `SNES` context
    2394: . func - function evaluation routine, see `SNESInitialGuessFn` for the calling sequence
    2395: - ctx  - [optional] user-defined context for private data for the
    2396:          function evaluation routine (may be `NULL`)

    2398:   Level: intermediate

    2400: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESInitialGuessFn`
    2401: @*/
    2402: PetscErrorCode SNESSetComputeInitialGuess(SNES snes, SNESInitialGuessFn *func, PetscCtx ctx)
    2403: {
    2404:   PetscFunctionBegin;
    2406:   if (func) snes->ops->computeinitialguess = func;
    2407:   if (ctx) snes->initialguessP = ctx;
    2408:   PetscFunctionReturn(PETSC_SUCCESS);
    2409: }

    2411: /*@C
    2412:   SNESGetRhs - Gets the vector for solving F(x) = `rhs`. If `rhs` is not set
    2413:   it assumes a zero right-hand side.

    2415:   Logically Collective

    2417:   Input Parameter:
    2418: . snes - the `SNES` context

    2420:   Output Parameter:
    2421: . rhs - the right-hand side vector or `NULL` if there is no right-hand side vector

    2423:   Level: intermediate

    2425: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`, `SNESComputeFunction()`, `SNESSetJacobian()`, `SNESSetFunction()`
    2426: @*/
    2427: PetscErrorCode SNESGetRhs(SNES snes, Vec *rhs)
    2428: {
    2429:   PetscFunctionBegin;
    2431:   PetscAssertPointer(rhs, 2);
    2432:   *rhs = snes->vec_rhs;
    2433:   PetscFunctionReturn(PETSC_SUCCESS);
    2434: }

    2436: /*@
    2437:   SNESComputeFunction - Calls the function that has been set with `SNESSetFunction()`.

    2439:   Collective

    2441:   Input Parameters:
    2442: + snes - the `SNES` context
    2443: - x    - input vector

    2445:   Output Parameter:
    2446: . f - function vector, as set by `SNESSetFunction()`

    2448:   Level: developer

    2450:   Notes:
    2451:   `SNESComputeFunction()` is typically used within nonlinear solvers
    2452:   implementations, so users would not generally call this routine themselves.

    2454:   When solving for $F(x) = b$, this routine computes $f = F(x) - b$.

    2456:   This function usually appears in the pattern.
    2457: .vb
    2458:   SNESComputeFunction(snes, x, f);
    2459:   VecNorm(f, &fnorm);
    2460:   SNESCheckFunctionDomainError(snes, fnorm); or SNESLineSearchCheckFunctionDomainError(ls, fnorm);
    2461: .ve
    2462:   to collectively handle the use of `SNESSetFunctionDomainError()` in the provided callback function.

    2464: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeMFFunction()`, `SNESSetFunctionDomainError()`
    2465: @*/
    2466: PetscErrorCode SNESComputeFunction(SNES snes, Vec x, Vec f)
    2467: {
    2468:   DM     dm;
    2469:   DMSNES sdm;

    2471:   PetscFunctionBegin;
    2475:   PetscCheckSameComm(snes, 1, x, 2);
    2476:   PetscCheckSameComm(snes, 1, f, 3);
    2477:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2479:   PetscCall(SNESGetDM(snes, &dm));
    2480:   PetscCall(DMGetDMSNES(dm, &sdm));
    2481:   PetscCheck(sdm->ops->computefunction || snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetFunction() or SNESSetDM() before SNESComputeFunction(), likely called from SNESSolve().");
    2482:   if (sdm->ops->computefunction) {
    2483:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, f, 0));
    2484:     PetscCall(VecLockReadPush(x));
    2485:     /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2486:     snes->functiondomainerror = PETSC_FALSE;
    2487:     {
    2488:       void           *ctx;
    2489:       SNESFunctionFn *computefunction;
    2490:       PetscCall(DMSNESGetFunction(dm, &computefunction, &ctx));
    2491:       PetscCallBack("SNES callback function", (*computefunction)(snes, x, f, ctx));
    2492:     }
    2493:     PetscCall(VecLockReadPop(x));
    2494:     if (sdm->ops->computefunction != SNESObjectiveComputeFunctionDefaultFD) PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, f, 0));
    2495:   } else /* if (snes->vec_rhs) */ {
    2496:     PetscCall(MatMult(snes->jacobian, x, f));
    2497:   }
    2498:   if (snes->vec_rhs) PetscCall(VecAXPY(f, -1.0, snes->vec_rhs));
    2499:   snes->nfuncs++;
    2500:   /*
    2501:      domainerror might not be set on all processes; so we tag vector locally with infinity and the next inner product or norm will
    2502:      propagate the value to all processes
    2503:   */
    2504:   PetscCall(VecFlag(f, snes->functiondomainerror));
    2505:   PetscFunctionReturn(PETSC_SUCCESS);
    2506: }

    2508: /*@
    2509:   SNESComputeMFFunction - Calls the function that has been set with `DMSNESSetMFFunction()`.

    2511:   Collective

    2513:   Input Parameters:
    2514: + snes - the `SNES` context
    2515: - x    - input vector

    2517:   Output Parameter:
    2518: . y - output vector

    2520:   Level: developer

    2522:   Notes:
    2523:   `SNESComputeMFFunction()` is used within the matrix-vector products called by the matrix created with `MatCreateSNESMF()`
    2524:   so users would not generally call this routine themselves.

    2526:   Since this function is intended for use with finite differencing it does not subtract the right-hand side vector provided with `SNESSolve()`
    2527:   while `SNESComputeFunction()` does. As such, this routine cannot be used with  `MatMFFDSetBase()` with a provided F function value even if it applies the
    2528:   same function as `SNESComputeFunction()` if a `SNESSolve()` right-hand side vector is use because the two functions difference would include this right hand side function.

    2530: .seealso: [](ch_snes), `SNES`, `SNESSetFunction()`, `SNESGetFunction()`, `SNESComputeFunction()`, `MatCreateSNESMF()`, `DMSNESSetMFFunction()`
    2531: @*/
    2532: PetscErrorCode SNESComputeMFFunction(SNES snes, Vec x, Vec y)
    2533: {
    2534:   DM     dm;
    2535:   DMSNES sdm;

    2537:   PetscFunctionBegin;
    2541:   PetscCheckSameComm(snes, 1, x, 2);
    2542:   PetscCheckSameComm(snes, 1, y, 3);
    2543:   PetscCall(VecValidValues_Internal(x, 2, PETSC_TRUE));

    2545:   PetscCall(SNESGetDM(snes, &dm));
    2546:   PetscCall(DMGetDMSNES(dm, &sdm));
    2547:   PetscCall(PetscLogEventBegin(SNES_FunctionEval, snes, x, y, 0));
    2548:   PetscCall(VecLockReadPush(x));
    2549:   /* ensure domainerror is false prior to computefunction evaluation (may not have been reset) */
    2550:   snes->functiondomainerror = PETSC_FALSE;
    2551:   PetscCallBack("SNES callback function", (*sdm->ops->computemffunction)(snes, x, y, sdm->mffunctionctx));
    2552:   PetscCall(VecLockReadPop(x));
    2553:   PetscCall(PetscLogEventEnd(SNES_FunctionEval, snes, x, y, 0));
    2554:   snes->nfuncs++;
    2555:   /*
    2556:      domainerror might not be set on all processes; so we tag vector locally with infinity and the next inner product or norm will
    2557:      propagate the value to all processes
    2558:   */
    2559:   PetscCall(VecFlag(y, snes->functiondomainerror));
    2560:   PetscFunctionReturn(PETSC_SUCCESS);
    2561: }

    2563: /*@
    2564:   SNESComputeNGS - Calls the Gauss-Seidel function that has been set with `SNESSetNGS()`.

    2566:   Collective

    2568:   Input Parameters:
    2569: + snes - the `SNES` context
    2570: . x    - input vector
    2571: - b    - rhs vector

    2573:   Output Parameter:
    2574: . x - new solution vector

    2576:   Level: developer

    2578:   Note:
    2579:   `SNESComputeNGS()` is typically used within composed nonlinear solver
    2580:   implementations, so most users would not generally call this routine
    2581:   themselves.

    2583: .seealso: [](ch_snes), `SNESNGSFn`, `SNESSetNGS()`, `SNESComputeFunction()`, `SNESNGS`
    2584: @*/
    2585: PetscErrorCode SNESComputeNGS(SNES snes, Vec b, Vec x)
    2586: {
    2587:   DM     dm;
    2588:   DMSNES sdm;

    2590:   PetscFunctionBegin;
    2594:   PetscCheckSameComm(snes, 1, x, 3);
    2595:   if (b) PetscCheckSameComm(snes, 1, b, 2);
    2596:   if (b) PetscCall(VecValidValues_Internal(b, 2, PETSC_TRUE));
    2597:   PetscCall(PetscLogEventBegin(SNES_NGSEval, snes, x, b, 0));
    2598:   PetscCall(SNESGetDM(snes, &dm));
    2599:   PetscCall(DMGetDMSNES(dm, &sdm));
    2600:   PetscCheck(sdm->ops->computegs, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "Must call SNESSetNGS() before SNESComputeNGS(), likely called from SNESSolve().");
    2601:   if (b) PetscCall(VecLockReadPush(b));
    2602:   PetscCallBack("SNES callback NGS", (*sdm->ops->computegs)(snes, x, b, sdm->gsctx));
    2603:   if (b) PetscCall(VecLockReadPop(b));
    2604:   PetscCall(PetscLogEventEnd(SNES_NGSEval, snes, x, b, 0));
    2605:   PetscFunctionReturn(PETSC_SUCCESS);
    2606: }

    2608: static PetscErrorCode SNESComputeFunction_FD(SNES snes, Vec Xin, Vec G)
    2609: {
    2610:   Vec          X;
    2611:   PetscScalar *g;
    2612:   PetscReal    f, f2;
    2613:   PetscInt     low, high, N, i;
    2614:   PetscBool    flg;
    2615:   PetscReal    h = .5 * PETSC_SQRT_MACHINE_EPSILON;

    2617:   PetscFunctionBegin;
    2618:   PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_fd_delta", &h, &flg));
    2619:   PetscCall(VecDuplicate(Xin, &X));
    2620:   PetscCall(VecCopy(Xin, X));
    2621:   PetscCall(VecGetSize(X, &N));
    2622:   PetscCall(VecGetOwnershipRange(X, &low, &high));
    2623:   PetscCall(VecSetOption(X, VEC_IGNORE_OFF_PROC_ENTRIES, PETSC_TRUE));
    2624:   PetscCall(VecGetArray(G, &g));
    2625:   for (i = 0; i < N; i++) {
    2626:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2627:     PetscCall(VecAssemblyBegin(X));
    2628:     PetscCall(VecAssemblyEnd(X));
    2629:     PetscCall(SNESComputeObjective(snes, X, &f));
    2630:     PetscCall(VecSetValue(X, i, 2.0 * h, ADD_VALUES));
    2631:     PetscCall(VecAssemblyBegin(X));
    2632:     PetscCall(VecAssemblyEnd(X));
    2633:     PetscCall(SNESComputeObjective(snes, X, &f2));
    2634:     PetscCall(VecSetValue(X, i, -h, ADD_VALUES));
    2635:     PetscCall(VecAssemblyBegin(X));
    2636:     PetscCall(VecAssemblyEnd(X));
    2637:     if (i >= low && i < high) g[i - low] = (f2 - f) / (2.0 * h);
    2638:   }
    2639:   PetscCall(VecRestoreArray(G, &g));
    2640:   PetscCall(VecDestroy(&X));
    2641:   PetscFunctionReturn(PETSC_SUCCESS);
    2642: }

    2644: /*@
    2645:   SNESTestFunction - Computes the difference between the computed and finite-difference functions

    2647:   Collective

    2649:   Input Parameter:
    2650: . snes - the `SNES` context

    2652:   Options Database Keys:
    2653: + -snes_test_function      - compare the user provided function with one compute via finite differences to check for errors.
    2654: - -snes_test_function_view - display the user provided function, the finite difference function and the difference

    2656:   Level: developer

    2658: .seealso: [](ch_snes), `SNESTestJacobian()`, `SNESSetFunction()`, `SNESComputeFunction()`
    2659: @*/
    2660: PetscErrorCode SNESTestFunction(SNES snes)
    2661: {
    2662:   Vec               x, g1, g2, g3;
    2663:   PetscBool         complete_print = PETSC_FALSE;
    2664:   PetscReal         hcnorm, fdnorm, hcmax, fdmax, diffmax, diffnorm;
    2665:   PetscScalar       dot;
    2666:   MPI_Comm          comm;
    2667:   PetscViewer       viewer, mviewer;
    2668:   PetscViewerFormat format;
    2669:   PetscInt          tabs;
    2670:   static PetscBool  directionsprinted = PETSC_FALSE;
    2671:   SNESObjectiveFn  *objective;

    2673:   PetscFunctionBegin;
    2674:   PetscCall(SNESGetObjective(snes, &objective, NULL));
    2675:   if (!objective) PetscFunctionReturn(PETSC_SUCCESS);

    2677:   PetscObjectOptionsBegin((PetscObject)snes);
    2678:   PetscCall(PetscOptionsViewer("-snes_test_function_view", "View difference between hand-coded and finite difference function element entries", "None", &mviewer, &format, &complete_print));
    2679:   PetscOptionsEnd();

    2681:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2682:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2683:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2684:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2685:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Function -------------\n"));
    2686:   if (!complete_print && !directionsprinted) {
    2687:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_function_view and optionally -snes_test_function <threshold> to show difference\n"));
    2688:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference function entries greater than <threshold>.\n"));
    2689:   }
    2690:   if (!directionsprinted) {
    2691:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Function, if (for double precision runs) ||F - Ffd||/||F|| is\n"));
    2692:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Function is probably correct.\n"));
    2693:     directionsprinted = PETSC_TRUE;
    2694:   }
    2695:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2697:   PetscCall(SNESGetSolution(snes, &x));
    2698:   PetscCall(VecDuplicate(x, &g1));
    2699:   PetscCall(VecDuplicate(x, &g2));
    2700:   PetscCall(VecDuplicate(x, &g3));
    2701:   PetscCall(SNESComputeFunction(snes, x, g1)); /* does not handle use of SNESSetFunctionDomainError() corrrectly */
    2702:   PetscCall(SNESComputeFunction_FD(snes, x, g2));

    2704:   PetscCall(VecNorm(g2, NORM_2, &fdnorm));
    2705:   PetscCall(VecNorm(g1, NORM_2, &hcnorm));
    2706:   PetscCall(VecNorm(g2, NORM_INFINITY, &fdmax));
    2707:   PetscCall(VecNorm(g1, NORM_INFINITY, &hcmax));
    2708:   PetscCall(VecDot(g1, g2, &dot));
    2709:   PetscCall(VecCopy(g1, g3));
    2710:   PetscCall(VecAXPY(g3, -1.0, g2));
    2711:   PetscCall(VecNorm(g3, NORM_2, &diffnorm));
    2712:   PetscCall(VecNorm(g3, NORM_INFINITY, &diffmax));
    2713:   PetscCall(PetscViewerASCIIPrintf(viewer, "  ||Ffd|| %g, ||F|| = %g, angle cosine = (Ffd'F)/||Ffd||||F|| = %g\n", (double)fdnorm, (double)hcnorm, (double)(PetscRealPart(dot) / (fdnorm * hcnorm))));
    2714:   PetscCall(PetscViewerASCIIPrintf(viewer, "  2-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffnorm / PetscMax(hcnorm, fdnorm)), (double)diffnorm));
    2715:   PetscCall(PetscViewerASCIIPrintf(viewer, "  max-norm ||F - Ffd||/||F|| = %g, ||F - Ffd|| = %g\n", (double)(diffmax / PetscMax(hcmax, fdmax)), (double)diffmax));

    2717:   if (complete_print) {
    2718:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded function ----------\n"));
    2719:     PetscCall(VecView(g1, mviewer));
    2720:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference function ----------\n"));
    2721:     PetscCall(VecView(g2, mviewer));
    2722:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference function ----------\n"));
    2723:     PetscCall(VecView(g3, mviewer));
    2724:   }
    2725:   PetscCall(VecDestroy(&g1));
    2726:   PetscCall(VecDestroy(&g2));
    2727:   PetscCall(VecDestroy(&g3));

    2729:   if (complete_print) {
    2730:     PetscCall(PetscViewerPopFormat(mviewer));
    2731:     PetscCall(PetscViewerDestroy(&mviewer));
    2732:   }
    2733:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));
    2734:   PetscFunctionReturn(PETSC_SUCCESS);
    2735: }

    2737: /*@
    2738:   SNESTestJacobian - Computes the difference between the computed and finite-difference Jacobians

    2740:   Collective

    2742:   Input Parameter:
    2743: . snes - the `SNES` context

    2745:   Output Parameters:
    2746: + Jnorm    - the Frobenius norm of the computed Jacobian, or `NULL`
    2747: - diffNorm - the Frobenius norm of the difference of the computed and finite-difference Jacobians, or `NULL`

    2749:   Options Database Keys:
    2750: + -snes_test_jacobian [threshold] - compare the user provided Jacobian with one compute via finite differences to check for errors.  If a threshold is given, display only those entries whose difference is greater than the threshold.
    2751: - -snes_test_jacobian_view        - display the user provided Jacobian, the finite difference Jacobian and the difference

    2753:   Level: developer

    2755:   Note:
    2756:   Directions and norms are printed to stdout if `diffNorm` is `NULL`.

    2758: .seealso: [](ch_snes), `SNESTestFunction()`, `SNESSetJacobian()`, `SNESComputeJacobian()`
    2759: @*/
    2760: PetscErrorCode SNESTestJacobian(SNES snes, PetscReal *Jnorm, PetscReal *diffNorm)
    2761: {
    2762:   Mat               A, B, C, D, jacobian;
    2763:   Vec               x = snes->vec_sol, f;
    2764:   PetscReal         nrm, gnorm;
    2765:   PetscReal         threshold = 1.e-5;
    2766:   void             *functx;
    2767:   PetscBool         complete_print = PETSC_FALSE, threshold_print = PETSC_FALSE, flg, istranspose;
    2768:   PetscBool         silent = diffNorm != PETSC_NULLPTR ? PETSC_TRUE : PETSC_FALSE;
    2769:   PetscViewer       viewer, mviewer;
    2770:   MPI_Comm          comm;
    2771:   PetscInt          tabs;
    2772:   static PetscBool  directionsprinted = PETSC_FALSE;
    2773:   PetscViewerFormat format;

    2775:   PetscFunctionBegin;
    2776:   PetscObjectOptionsBegin((PetscObject)snes);
    2777:   PetscCall(PetscOptionsReal("-snes_test_jacobian", "Threshold for element difference between hand-coded and finite difference being meaningful", "None", threshold, &threshold, NULL));
    2778:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display", "-snes_test_jacobian_view", "3.13", NULL));
    2779:   PetscCall(PetscOptionsViewer("-snes_test_jacobian_view", "View difference between hand-coded and finite difference Jacobians element entries", "None", &mviewer, &format, &complete_print));
    2780:   PetscCall(PetscOptionsDeprecated("-snes_test_jacobian_display_threshold", "-snes_test_jacobian", "3.13", "-snes_test_jacobian accepts an optional threshold (since v3.10)"));
    2781:   PetscCall(PetscOptionsReal("-snes_test_jacobian_display_threshold", "Display difference between hand-coded and finite difference Jacobians which exceed input threshold", "None", threshold, &threshold, &threshold_print));
    2782:   PetscOptionsEnd();

    2784:   PetscCall(PetscObjectGetComm((PetscObject)snes, &comm));
    2785:   PetscCall(PetscViewerASCIIGetStdout(comm, &viewer));
    2786:   PetscCall(PetscViewerASCIIGetTab(viewer, &tabs));
    2787:   PetscCall(PetscViewerASCIISetTab(viewer, ((PetscObject)snes)->tablevel));
    2788:   if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian -------------\n"));
    2789:   if (!complete_print && !silent && !directionsprinted) {
    2790:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Run with -snes_test_jacobian_view and optionally -snes_test_jacobian <threshold> to show difference\n"));
    2791:     PetscCall(PetscViewerASCIIPrintf(viewer, "    of hand-coded and finite difference Jacobian entries greater than <threshold>.\n"));
    2792:   }
    2793:   if (!directionsprinted && !silent) {
    2794:     PetscCall(PetscViewerASCIIPrintf(viewer, "  Testing hand-coded Jacobian, if (for double precision runs) ||J - Jfd||_F/||J||_F is\n"));
    2795:     PetscCall(PetscViewerASCIIPrintf(viewer, "    O(1.e-8), the hand-coded Jacobian is probably correct.\n"));
    2796:     directionsprinted = PETSC_TRUE;
    2797:   }
    2798:   if (complete_print) PetscCall(PetscViewerPushFormat(mviewer, format));

    2800:   PetscCall(PetscObjectTypeCompare((PetscObject)snes->jacobian, MATMFFD, &flg));
    2801:   if (!flg) jacobian = snes->jacobian;
    2802:   else jacobian = snes->jacobian_pre;

    2804:   if (!x) PetscCall(MatCreateVecs(jacobian, &x, NULL));
    2805:   else PetscCall(PetscObjectReference((PetscObject)x));
    2806:   PetscCall(VecDuplicate(x, &f));

    2808:   /* evaluate the function at this point because SNESComputeJacobianDefault() assumes that the function has been evaluated and put into snes->vec_func */
    2809:   PetscCall(SNESComputeFunction(snes, x, f));
    2810:   PetscCall(VecDestroy(&f));
    2811:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, SNESKSPTRANSPOSEONLY, &istranspose));
    2812:   while (jacobian) {
    2813:     Mat JT = NULL, Jsave = NULL;

    2815:     if (istranspose) {
    2816:       PetscCall(MatCreateTranspose(jacobian, &JT));
    2817:       Jsave    = jacobian;
    2818:       jacobian = JT;
    2819:     }
    2820:     PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)jacobian, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    2821:     if (flg) {
    2822:       A = jacobian;
    2823:       PetscCall(PetscObjectReference((PetscObject)A));
    2824:     } else {
    2825:       PetscCall(MatComputeOperator(jacobian, MATAIJ, &A));
    2826:     }

    2828:     PetscCall(MatDuplicate(A, MAT_DO_NOT_COPY_VALUES, &B));
    2829:     PetscCall(MatSetOption(B, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2831:     PetscCall(SNESGetFunction(snes, NULL, NULL, &functx));
    2832:     PetscCall(SNESComputeJacobianDefault(snes, x, B, B, functx));

    2834:     PetscCall(MatDuplicate(B, MAT_COPY_VALUES, &D));
    2835:     PetscCall(MatAYPX(D, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2836:     PetscCall(MatNorm(D, NORM_FROBENIUS, &nrm));
    2837:     PetscCall(MatNorm(A, NORM_FROBENIUS, &gnorm));
    2838:     PetscCall(MatDestroy(&D));
    2839:     if (!gnorm) gnorm = 1; /* just in case */
    2840:     if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ||J - Jfd||_F/||J||_F = %g, ||J - Jfd||_F = %g\n", (double)(nrm / gnorm), (double)nrm));
    2841:     if (complete_print) {
    2842:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded Jacobian ----------\n"));
    2843:       PetscCall(MatView(A, mviewer));
    2844:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Finite difference Jacobian ----------\n"));
    2845:       PetscCall(MatView(B, mviewer));
    2846:     }

    2848:     if (threshold_print || complete_print) {
    2849:       PetscInt           Istart, Iend, *ccols, bncols, cncols, j, row;
    2850:       PetscScalar       *cvals;
    2851:       const PetscInt    *bcols;
    2852:       const PetscScalar *bvals;

    2854:       PetscCall(MatDuplicate(A, MAT_DO_NOT_COPY_VALUES, &C));
    2855:       PetscCall(MatSetOption(C, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_FALSE));

    2857:       PetscCall(MatAYPX(B, -1.0, A, DIFFERENT_NONZERO_PATTERN));
    2858:       PetscCall(MatGetOwnershipRange(B, &Istart, &Iend));

    2860:       for (row = Istart; row < Iend; row++) {
    2861:         PetscCall(MatGetRow(B, row, &bncols, &bcols, &bvals));
    2862:         PetscCall(PetscMalloc2(bncols, &ccols, bncols, &cvals));
    2863:         for (j = 0, cncols = 0; j < bncols; j++) {
    2864:           if (PetscAbsScalar(bvals[j]) > threshold) {
    2865:             ccols[cncols] = bcols[j];
    2866:             cvals[cncols] = bvals[j];
    2867:             cncols += 1;
    2868:           }
    2869:         }
    2870:         if (cncols) PetscCall(MatSetValues(C, 1, &row, cncols, ccols, cvals, INSERT_VALUES));
    2871:         PetscCall(MatRestoreRow(B, row, &bncols, &bcols, &bvals));
    2872:         PetscCall(PetscFree2(ccols, cvals));
    2873:       }
    2874:       PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
    2875:       PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
    2876:       PetscCall(PetscViewerASCIIPrintf(viewer, "  Hand-coded minus finite-difference Jacobian with tolerance %g ----------\n", (double)threshold));
    2877:       PetscCall(MatView(C, complete_print ? mviewer : viewer));
    2878:       PetscCall(MatDestroy(&C));
    2879:     }
    2880:     PetscCall(MatDestroy(&A));
    2881:     PetscCall(MatDestroy(&B));
    2882:     PetscCall(MatDestroy(&JT));
    2883:     if (Jsave) jacobian = Jsave;
    2884:     if (jacobian != snes->jacobian_pre) {
    2885:       jacobian = snes->jacobian_pre;
    2886:       if (!silent) PetscCall(PetscViewerASCIIPrintf(viewer, "  ---------- Testing Jacobian for preconditioner -------------\n"));
    2887:     } else jacobian = NULL;
    2888:   }
    2889:   PetscCall(VecDestroy(&x));
    2890:   if (complete_print) PetscCall(PetscViewerPopFormat(mviewer));
    2891:   PetscCall(PetscViewerDestroy(&mviewer));
    2892:   PetscCall(PetscViewerASCIISetTab(viewer, tabs));

    2894:   if (Jnorm) *Jnorm = gnorm;
    2895:   if (diffNorm) *diffNorm = nrm;
    2896:   PetscFunctionReturn(PETSC_SUCCESS);
    2897: }

    2899: /*@
    2900:   SNESComputeJacobian - Computes the Jacobian matrix that has been set with `SNESSetJacobian()`.

    2902:   Collective

    2904:   Input Parameters:
    2905: + snes - the `SNES` context
    2906: - X    - input vector

    2908:   Output Parameters:
    2909: + A - Jacobian matrix
    2910: - B - optional matrix for building the preconditioner, usually the same as `A`

    2912:   Options Database Keys:
    2913: + -snes_lag_preconditioner lag          - how often to rebuild preconditioner
    2914: . -snes_lag_jacobian lag                - how often to rebuild Jacobian
    2915: . -snes_test_jacobian [threshold]       - compare the user provided Jacobian with one compute via finite differences to check for errors.
    2916:                                           If a threshold is given, display only those entries whose difference is greater than the threshold.
    2917: . -snes_test_jacobian_view [viewer]     - display the user provided Jacobian, the finite difference Jacobian and the difference between them to help users detect the location of errors in the user provided Jacobian
    2918: . -snes_compare_explicit                - Compare the computed Jacobian to the finite difference Jacobian and output the differences
    2919: . -snes_compare_explicit_draw           - Compare the computed Jacobian to the finite difference Jacobian and draw the result
    2920: . -snes_compare_explicit_contour        - Compare the computed Jacobian to the finite difference Jacobian and draw a contour plot with the result
    2921: . -snes_compare_operator                - Make the comparison options above use the operator instead of the matrix used to construct the preconditioner
    2922: . -snes_compare_coloring                - Compute the finite difference Jacobian using coloring and display norms of difference
    2923: . -snes_compare_coloring_display        - Compute the finite difference Jacobian using coloring and display verbose differences
    2924: . -snes_compare_coloring_threshold      - Display only those matrix entries that differ by more than a given threshold
    2925: . -snes_compare_coloring_threshold_atol - Absolute tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2926: . -snes_compare_coloring_threshold_rtol - Relative tolerance for difference in matrix entries to be displayed by `-snes_compare_coloring_threshold`
    2927: . -snes_compare_coloring_draw           - Compute the finite difference Jacobian using coloring and draw differences
    2928: - -snes_compare_coloring_draw_contour   - Compute the finite difference Jacobian using coloring and show contours of matrices and differences

    2930:   Level: developer

    2932:   Note:
    2933:   Most users should not need to explicitly call this routine, as it
    2934:   is used internally within the nonlinear solvers.

    2936:   Developer Note:
    2937:   This has duplicative ways of checking the accuracy of the user provided Jacobian (see the options above). This is for historical reasons, the routine `SNESTestJacobian()` use to used
    2938:   with the `SNESType` of test that has been removed.

    2940: .seealso: [](ch_snes), `SNESSetJacobian()`, `KSPSetOperators()`, `MatStructure`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobian()`,
    2941:           `SNESSetJacobianDomainError()`, `SNESCheckJacobianDomainError()`, `SNESSetCheckJacobianDomainError()`
    2942: @*/
    2943: PetscErrorCode SNESComputeJacobian(SNES snes, Vec X, Mat A, Mat B)
    2944: {
    2945:   PetscBool flag;
    2946:   DM        dm;
    2947:   DMSNES    sdm;
    2948:   KSP       ksp;

    2950:   PetscFunctionBegin;
    2953:   PetscCheckSameComm(snes, 1, X, 2);
    2954:   PetscCall(VecValidValues_Internal(X, 2, PETSC_TRUE));
    2955:   PetscCall(SNESGetDM(snes, &dm));
    2956:   PetscCall(DMGetDMSNES(dm, &sdm));

    2958:   /* make sure that MatAssemblyBegin/End() is called on A matrix if it is matrix-free */
    2959:   if (snes->lagjacobian == -2) {
    2960:     snes->lagjacobian = -1;

    2962:     PetscCall(PetscInfo(snes, "Recomputing Jacobian/preconditioner because lag is -2 (means compute Jacobian, but then never again) \n"));
    2963:   } else if (snes->lagjacobian == -1) {
    2964:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is -1\n"));
    2965:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2966:     if (flag) {
    2967:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2968:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2969:     }
    2970:     PetscFunctionReturn(PETSC_SUCCESS);
    2971:   } else if (snes->lagjacobian > 1 && (snes->iter + snes->jac_iter) % snes->lagjacobian) {
    2972:     PetscCall(PetscInfo(snes, "Reusing Jacobian/preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagjacobian, snes->iter));
    2973:     PetscCall(PetscObjectTypeCompare((PetscObject)A, MATMFFD, &flag));
    2974:     if (flag) {
    2975:       PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2976:       PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2977:     }
    2978:     PetscFunctionReturn(PETSC_SUCCESS);
    2979:   }
    2980:   if (snes->npc && snes->npcside == PC_LEFT) {
    2981:     PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
    2982:     PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
    2983:     PetscFunctionReturn(PETSC_SUCCESS);
    2984:   }

    2986:   PetscCall(PetscLogEventBegin(SNES_JacobianEval, snes, X, A, B));
    2987:   PetscCall(VecLockReadPush(X));
    2988:   {
    2989:     void           *ctx;
    2990:     SNESJacobianFn *J;
    2991:     PetscCall(DMSNESGetJacobian(dm, &J, &ctx));
    2992:     PetscCallBack("SNES callback Jacobian", (*J)(snes, X, A, B, ctx));
    2993:   }
    2994:   PetscCall(VecLockReadPop(X));
    2995:   PetscCall(PetscLogEventEnd(SNES_JacobianEval, snes, X, A, B));

    2997:   /* attach latest linearization point to the matrix used to construct the preconditioner */
    2998:   PetscCall(PetscObjectCompose((PetscObject)B, "__SNES_latest_X", (PetscObject)X));

    3000:   /* the next line ensures that snes->ksp exists */
    3001:   PetscCall(SNESGetKSP(snes, &ksp));
    3002:   if (snes->lagpreconditioner == -2) {
    3003:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner exactly once since lag is -2\n"));
    3004:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3005:     snes->lagpreconditioner = -1;
    3006:   } else if (snes->lagpreconditioner == -1) {
    3007:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is -1\n"));
    3008:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3009:   } else if (snes->lagpreconditioner > 1 && (snes->iter + snes->pre_iter) % snes->lagpreconditioner) {
    3010:     PetscCall(PetscInfo(snes, "Reusing preconditioner because lag is %" PetscInt_FMT " and SNES iteration is %" PetscInt_FMT "\n", snes->lagpreconditioner, snes->iter));
    3011:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_TRUE));
    3012:   } else {
    3013:     PetscCall(PetscInfo(snes, "Rebuilding preconditioner\n"));
    3014:     PetscCall(KSPSetReusePreconditioner(snes->ksp, PETSC_FALSE));
    3015:   }

    3017:   /* monkey business to allow testing Jacobians in multilevel solvers.
    3018:      This is needed because the SNESTestXXX interface does not accept vectors and matrices */
    3019:   {
    3020:     Vec xsave            = snes->vec_sol;
    3021:     Mat jacobiansave     = snes->jacobian;
    3022:     Mat jacobian_presave = snes->jacobian_pre;

    3024:     snes->vec_sol      = X;
    3025:     snes->jacobian     = A;
    3026:     snes->jacobian_pre = B;
    3027:     if (snes->testFunc) PetscCall(SNESTestFunction(snes));
    3028:     if (snes->testJac) PetscCall(SNESTestJacobian(snes, NULL, NULL));

    3030:     snes->vec_sol      = xsave;
    3031:     snes->jacobian     = jacobiansave;
    3032:     snes->jacobian_pre = jacobian_presave;
    3033:   }

    3035:   {
    3036:     PetscBool flag = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_operator = PETSC_FALSE;
    3037:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit", NULL, NULL, &flag));
    3038:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw", NULL, NULL, &flag_draw));
    3039:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_explicit_draw_contour", NULL, NULL, &flag_contour));
    3040:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_operator", NULL, NULL, &flag_operator));
    3041:     if (flag || flag_draw || flag_contour) {
    3042:       Mat         Bexp_mine = NULL, Bexp, FDexp;
    3043:       PetscViewer vdraw, vstdout;
    3044:       PetscBool   flg;
    3045:       if (flag_operator) {
    3046:         PetscCall(MatComputeOperator(A, MATAIJ, &Bexp_mine));
    3047:         Bexp = Bexp_mine;
    3048:       } else {
    3049:         /* See if the matrix used to construct the preconditioner can be viewed and added directly */
    3050:         PetscCall(PetscObjectBaseTypeCompareAny((PetscObject)B, &flg, MATSEQAIJ, MATMPIAIJ, MATSEQDENSE, MATMPIDENSE, MATSEQBAIJ, MATMPIBAIJ, MATSEQSBAIJ, MATMPISBAIJ, ""));
    3051:         if (flg) Bexp = B;
    3052:         else {
    3053:           /* If the "preconditioning" matrix is itself MATSHELL or some other type without direct support */
    3054:           PetscCall(MatComputeOperator(B, MATAIJ, &Bexp_mine));
    3055:           Bexp = Bexp_mine;
    3056:         }
    3057:       }
    3058:       PetscCall(MatConvert(Bexp, MATSAME, MAT_INITIAL_MATRIX, &FDexp));
    3059:       PetscCall(SNESComputeJacobianDefault(snes, X, FDexp, FDexp, NULL));
    3060:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3061:       if (flag_draw || flag_contour) {
    3062:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Explicit Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3063:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3064:       } else vdraw = NULL;
    3065:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit %s\n", flag_operator ? "Jacobian" : "preconditioning Jacobian"));
    3066:       if (flag) PetscCall(MatView(Bexp, vstdout));
    3067:       if (vdraw) PetscCall(MatView(Bexp, vdraw));
    3068:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Finite difference Jacobian\n"));
    3069:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3070:       if (vdraw) PetscCall(MatView(FDexp, vdraw));
    3071:       PetscCall(MatAYPX(FDexp, -1.0, Bexp, SAME_NONZERO_PATTERN));
    3072:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian\n"));
    3073:       if (flag) PetscCall(MatView(FDexp, vstdout));
    3074:       if (vdraw) { /* Always use contour for the difference */
    3075:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3076:         PetscCall(MatView(FDexp, vdraw));
    3077:         PetscCall(PetscViewerPopFormat(vdraw));
    3078:       }
    3079:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));
    3080:       PetscCall(PetscViewerDestroy(&vdraw));
    3081:       PetscCall(MatDestroy(&Bexp_mine));
    3082:       PetscCall(MatDestroy(&FDexp));
    3083:     }
    3084:   }
    3085:   {
    3086:     PetscBool flag = PETSC_FALSE, flag_display = PETSC_FALSE, flag_draw = PETSC_FALSE, flag_contour = PETSC_FALSE, flag_threshold = PETSC_FALSE;
    3087:     PetscReal threshold_atol = PETSC_SQRT_MACHINE_EPSILON, threshold_rtol = 10 * PETSC_SQRT_MACHINE_EPSILON;
    3088:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring", NULL, NULL, &flag));
    3089:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_display", NULL, NULL, &flag_display));
    3090:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw", NULL, NULL, &flag_draw));
    3091:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_draw_contour", NULL, NULL, &flag_contour));
    3092:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold", NULL, NULL, &flag_threshold));
    3093:     if (flag_threshold) {
    3094:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_rtol", &threshold_rtol, NULL));
    3095:       PetscCall(PetscOptionsGetReal(((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_compare_coloring_threshold_atol", &threshold_atol, NULL));
    3096:     }
    3097:     if (flag || flag_display || flag_draw || flag_contour || flag_threshold) {
    3098:       Mat             Bfd;
    3099:       PetscViewer     vdraw, vstdout;
    3100:       MatColoring     coloring;
    3101:       ISColoring      iscoloring;
    3102:       MatFDColoring   matfdcoloring;
    3103:       SNESFunctionFn *func;
    3104:       void           *funcctx;
    3105:       PetscReal       norm1, norm2, normmax;

    3107:       PetscCall(MatDuplicate(B, MAT_DO_NOT_COPY_VALUES, &Bfd));
    3108:       PetscCall(MatColoringCreate(Bfd, &coloring));
    3109:       PetscCall(MatColoringSetType(coloring, MATCOLORINGSL));
    3110:       PetscCall(MatColoringSetFromOptions(coloring));
    3111:       PetscCall(MatColoringApply(coloring, &iscoloring));
    3112:       PetscCall(MatColoringDestroy(&coloring));
    3113:       PetscCall(MatFDColoringCreate(Bfd, iscoloring, &matfdcoloring));
    3114:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3115:       PetscCall(MatFDColoringSetUp(Bfd, iscoloring, matfdcoloring));
    3116:       PetscCall(ISColoringDestroy(&iscoloring));

    3118:       /* This method of getting the function is currently unreliable since it doesn't work for DM local functions. */
    3119:       PetscCall(SNESGetFunction(snes, NULL, &func, &funcctx));
    3120:       PetscCall(MatFDColoringSetFunction(matfdcoloring, (MatFDColoringFn *)func, funcctx));
    3121:       PetscCall(PetscObjectSetOptionsPrefix((PetscObject)matfdcoloring, ((PetscObject)snes)->prefix));
    3122:       PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)matfdcoloring, "coloring_"));
    3123:       PetscCall(MatFDColoringSetFromOptions(matfdcoloring));
    3124:       PetscCall(MatFDColoringApply(Bfd, matfdcoloring, X, snes));
    3125:       PetscCall(MatFDColoringDestroy(&matfdcoloring));

    3127:       PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)snes), &vstdout));
    3128:       if (flag_draw || flag_contour) {
    3129:         PetscCall(PetscViewerDrawOpen(PetscObjectComm((PetscObject)snes), NULL, "Colored Jacobians", PETSC_DECIDE, PETSC_DECIDE, 300, 300, &vdraw));
    3130:         if (flag_contour) PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3131:       } else vdraw = NULL;
    3132:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Explicit preconditioning Jacobian\n"));
    3133:       if (flag_display) PetscCall(MatView(B, vstdout));
    3134:       if (vdraw) PetscCall(MatView(B, vdraw));
    3135:       PetscCall(PetscViewerASCIIPrintf(vstdout, "Colored Finite difference Jacobian\n"));
    3136:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3137:       if (vdraw) PetscCall(MatView(Bfd, vdraw));
    3138:       PetscCall(MatAYPX(Bfd, -1.0, B, SAME_NONZERO_PATTERN));
    3139:       PetscCall(MatNorm(Bfd, NORM_1, &norm1));
    3140:       PetscCall(MatNorm(Bfd, NORM_FROBENIUS, &norm2));
    3141:       PetscCall(MatNorm(Bfd, NORM_MAX, &normmax));
    3142:       PetscCall(PetscViewerASCIIPrintf(vstdout, "User-provided matrix minus finite difference Jacobian, norm1=%g normFrob=%g normmax=%g\n", (double)norm1, (double)norm2, (double)normmax));
    3143:       if (flag_display) PetscCall(MatView(Bfd, vstdout));
    3144:       if (vdraw) { /* Always use contour for the difference */
    3145:         PetscCall(PetscViewerPushFormat(vdraw, PETSC_VIEWER_DRAW_CONTOUR));
    3146:         PetscCall(MatView(Bfd, vdraw));
    3147:         PetscCall(PetscViewerPopFormat(vdraw));
    3148:       }
    3149:       if (flag_contour) PetscCall(PetscViewerPopFormat(vdraw));

    3151:       if (flag_threshold) {
    3152:         PetscInt bs, rstart, rend, i;
    3153:         PetscCall(MatGetBlockSize(B, &bs));
    3154:         PetscCall(MatGetOwnershipRange(B, &rstart, &rend));
    3155:         for (i = rstart; i < rend; i++) {
    3156:           const PetscScalar *ba, *ca;
    3157:           const PetscInt    *bj, *cj;
    3158:           PetscInt           bn, cn, j, maxentrycol = -1, maxdiffcol = -1, maxrdiffcol = -1;
    3159:           PetscReal          maxentry = 0, maxdiff = 0, maxrdiff = 0;
    3160:           PetscCall(MatGetRow(B, i, &bn, &bj, &ba));
    3161:           PetscCall(MatGetRow(Bfd, i, &cn, &cj, &ca));
    3162:           PetscCheck(bn == cn, ((PetscObject)A)->comm, PETSC_ERR_PLIB, "Unexpected different nonzero pattern in -snes_compare_coloring_threshold");
    3163:           for (j = 0; j < bn; j++) {
    3164:             PetscReal rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3165:             if (PetscAbsScalar(ba[j]) > PetscAbs(maxentry)) {
    3166:               maxentrycol = bj[j];
    3167:               maxentry    = PetscRealPart(ba[j]);
    3168:             }
    3169:             if (PetscAbsScalar(ca[j]) > PetscAbs(maxdiff)) {
    3170:               maxdiffcol = bj[j];
    3171:               maxdiff    = PetscRealPart(ca[j]);
    3172:             }
    3173:             if (rdiff > maxrdiff) {
    3174:               maxrdiffcol = bj[j];
    3175:               maxrdiff    = rdiff;
    3176:             }
    3177:           }
    3178:           if (maxrdiff > 1) {
    3179:             PetscCall(PetscViewerASCIIPrintf(vstdout, "row %" PetscInt_FMT " (maxentry=%g at %" PetscInt_FMT ", maxdiff=%g at %" PetscInt_FMT ", maxrdiff=%g at %" PetscInt_FMT "):", i, (double)maxentry, maxentrycol, (double)maxdiff, maxdiffcol, (double)maxrdiff, maxrdiffcol));
    3180:             for (j = 0; j < bn; j++) {
    3181:               PetscReal rdiff;
    3182:               rdiff = PetscAbsScalar(ca[j]) / (threshold_atol + threshold_rtol * PetscAbsScalar(ba[j]));
    3183:               if (rdiff > 1) PetscCall(PetscViewerASCIIPrintf(vstdout, " (%" PetscInt_FMT ",%g:%g)", bj[j], (double)PetscRealPart(ba[j]), (double)PetscRealPart(ca[j])));
    3184:             }
    3185:             PetscCall(PetscViewerASCIIPrintf(vstdout, "\n"));
    3186:           }
    3187:           PetscCall(MatRestoreRow(B, i, &bn, &bj, &ba));
    3188:           PetscCall(MatRestoreRow(Bfd, i, &cn, &cj, &ca));
    3189:         }
    3190:       }
    3191:       PetscCall(PetscViewerDestroy(&vdraw));
    3192:       PetscCall(MatDestroy(&Bfd));
    3193:     }
    3194:   }
    3195:   PetscFunctionReturn(PETSC_SUCCESS);
    3196: }

    3198: /*@C
    3199:   SNESSetJacobian - Sets the function to compute Jacobian as well as the
    3200:   location to store the matrix.

    3202:   Logically Collective

    3204:   Input Parameters:
    3205: + snes - the `SNES` context
    3206: . Amat - the matrix that defines the (approximate) Jacobian
    3207: . Pmat - the matrix to be used in constructing the preconditioner, usually the same as `Amat`.
    3208: . J    - Jacobian evaluation routine (if `NULL` then `SNES` retains any previously set value), see `SNESJacobianFn` for details
    3209: - ctx  - [optional] user-defined context for private data for the
    3210:          Jacobian evaluation routine (may be `NULL`) (if `NULL` then `SNES` retains any previously set value)

    3212:   Level: beginner

    3214:   Notes:
    3215:   If the `Amat` matrix and `Pmat` matrix are different you must call `MatAssemblyBegin()`/`MatAssemblyEnd()` on
    3216:   each matrix.

    3218:   If you know the operator `Amat` has a null space you can use `MatSetNullSpace()` and `MatSetTransposeNullSpace()` to supply the null
    3219:   space to `Amat` and the `KSP` solvers will automatically use that null space as needed during the solution process.

    3221:   If using `SNESComputeJacobianDefaultColor()` to assemble a Jacobian, the `ctx` argument
    3222:   must be a `MatFDColoring`.

    3224:   Other defect-correction schemes can be used by computing a different matrix in place of the Jacobian.  One common
    3225:   example is to use the "Picard linearization" which only differentiates through the highest order parts of each term using `SNESSetPicard()`

    3227: .seealso: [](ch_snes), `SNES`, `KSPSetOperators()`, `SNESSetFunction()`, `MatMFFDComputeJacobian()`, `SNESComputeJacobianDefaultColor()`, `MatStructure`,
    3228:           `SNESSetPicard()`, `SNESJacobianFn`, `SNESFunctionFn`
    3229: @*/
    3230: PetscErrorCode SNESSetJacobian(SNES snes, Mat Amat, Mat Pmat, SNESJacobianFn *J, PetscCtx ctx)
    3231: {
    3232:   DM dm;

    3234:   PetscFunctionBegin;
    3238:   if (Amat) PetscCheckSameComm(snes, 1, Amat, 2);
    3239:   if (Pmat) PetscCheckSameComm(snes, 1, Pmat, 3);
    3240:   PetscCall(SNESGetDM(snes, &dm));
    3241:   PetscCall(DMSNESSetJacobian(dm, J, ctx));
    3242:   if (Amat) {
    3243:     PetscCall(PetscObjectReference((PetscObject)Amat));
    3244:     PetscCall(MatDestroy(&snes->jacobian));

    3246:     snes->jacobian = Amat;
    3247:   }
    3248:   if (Pmat) {
    3249:     PetscCall(PetscObjectReference((PetscObject)Pmat));
    3250:     PetscCall(MatDestroy(&snes->jacobian_pre));

    3252:     snes->jacobian_pre = Pmat;
    3253:   }
    3254:   PetscFunctionReturn(PETSC_SUCCESS);
    3255: }

    3257: /*@C
    3258:   SNESGetJacobian - Returns the Jacobian matrix and optionally the user
    3259:   provided context for evaluating the Jacobian.

    3261:   Not Collective, but `Mat` object will be parallel if `SNES` is

    3263:   Input Parameter:
    3264: . snes - the nonlinear solver context

    3266:   Output Parameters:
    3267: + Amat - location to stash (approximate) Jacobian matrix (or `NULL`)
    3268: . Pmat - location to stash matrix used to compute the preconditioner (or `NULL`)
    3269: . J    - location to put Jacobian function (or `NULL`), for calling sequence see `SNESJacobianFn`
    3270: - ctx  - location to stash Jacobian ctx (or `NULL`)

    3272:   Level: advanced

    3274: .seealso: [](ch_snes), `SNES`, `Mat`, `SNESSetJacobian()`, `SNESComputeJacobian()`, `SNESJacobianFn`, `SNESGetFunction()`
    3275: @*/
    3276: PetscErrorCode SNESGetJacobian(SNES snes, Mat *Amat, Mat *Pmat, SNESJacobianFn **J, PetscCtxRt ctx)
    3277: {
    3278:   DM dm;

    3280:   PetscFunctionBegin;
    3282:   if (Amat) *Amat = snes->jacobian;
    3283:   if (Pmat) *Pmat = snes->jacobian_pre;
    3284:   PetscCall(SNESGetDM(snes, &dm));
    3285:   PetscCall(DMSNESGetJacobian(dm, J, ctx));
    3286:   PetscFunctionReturn(PETSC_SUCCESS);
    3287: }

    3289: static PetscErrorCode SNESSetDefaultComputeJacobian(SNES snes)
    3290: {
    3291:   DM     dm;
    3292:   DMSNES sdm;

    3294:   PetscFunctionBegin;
    3295:   PetscCall(SNESGetDM(snes, &dm));
    3296:   PetscCall(DMGetDMSNES(dm, &sdm));
    3297:   if (!sdm->ops->computejacobian && snes->jacobian_pre) {
    3298:     DM        dm;
    3299:     PetscBool isdense, ismf;

    3301:     PetscCall(SNESGetDM(snes, &dm));
    3302:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &isdense, MATSEQDENSE, MATMPIDENSE, MATDENSE, NULL));
    3303:     PetscCall(PetscObjectTypeCompareAny((PetscObject)snes->jacobian_pre, &ismf, MATMFFD, MATSHELL, NULL));
    3304:     if (isdense) PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefault, NULL));
    3305:     else if (!ismf) PetscCall(DMSNESSetJacobian(dm, SNESComputeJacobianDefaultColor, NULL));
    3306:   }
    3307:   PetscFunctionReturn(PETSC_SUCCESS);
    3308: }

    3310: /*@
    3311:   SNESSetUp - Sets up the internal data structures for the later use
    3312:   of a nonlinear solver `SNESSolve()`.

    3314:   Collective

    3316:   Input Parameter:
    3317: . snes - the `SNES` context

    3319:   Level: advanced

    3321:   Note:
    3322:   For basic use of the `SNES` solvers the user does not need to explicitly call
    3323:   `SNESSetUp()`, since these actions will automatically occur during
    3324:   the call to `SNESSolve()`.  However, if one wishes to control this
    3325:   phase separately, `SNESSetUp()` should be called after `SNESCreate()`
    3326:   and optional routines of the form SNESSetXXX(), but before `SNESSolve()`.

    3328: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`, `SNESDestroy()`, `SNESSetFromOptions()`
    3329: @*/
    3330: PetscErrorCode SNESSetUp(SNES snes)
    3331: {
    3332:   DM             dm;
    3333:   DMSNES         sdm;
    3334:   SNESLineSearch linesearch, pclinesearch;
    3335:   void          *lsprectx, *lspostctx;
    3336:   PetscBool      mf_operator, mf;
    3337:   Vec            f, fpc;
    3338:   void          *funcctx;
    3339:   void          *jacctx, *appctx;
    3340:   Mat            j, jpre;
    3341:   PetscErrorCode (*precheck)(SNESLineSearch, Vec, Vec, PetscBool *, PetscCtx);
    3342:   PetscErrorCode (*postcheck)(SNESLineSearch, Vec, Vec, Vec, PetscBool *, PetscBool *, PetscCtx);
    3343:   SNESFunctionFn *func;
    3344:   SNESJacobianFn *jac;

    3346:   PetscFunctionBegin;
    3348:   if (snes->setupcalled) PetscFunctionReturn(PETSC_SUCCESS);
    3349:   PetscCall(PetscLogEventBegin(SNES_SetUp, snes, 0, 0, 0));

    3351:   if (!((PetscObject)snes)->type_name) PetscCall(SNESSetType(snes, SNESNEWTONLS));

    3353:   PetscCall(SNESGetFunction(snes, &snes->vec_func, NULL, NULL));

    3355:   PetscCall(SNESGetDM(snes, &dm));
    3356:   PetscCall(DMGetDMSNES(dm, &sdm));
    3357:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3359:   if (!snes->vec_func) PetscCall(DMCreateGlobalVector(dm, &snes->vec_func));

    3361:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));

    3363:   if (snes->linesearch) {
    3364:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    3365:     PetscCall(SNESLineSearchSetFunction(snes->linesearch, SNESComputeFunction));
    3366:   }

    3368:   PetscCall(SNESGetUseMatrixFree(snes, &mf_operator, &mf));
    3369:   if (snes->npc && snes->npcside == PC_LEFT) {
    3370:     snes->mf          = PETSC_TRUE;
    3371:     snes->mf_operator = PETSC_FALSE;
    3372:   }

    3374:   if (snes->npc) {
    3375:     /* copy the DM over */
    3376:     PetscCall(SNESGetDM(snes, &dm));
    3377:     PetscCall(SNESSetDM(snes->npc, dm));

    3379:     PetscCall(SNESGetFunction(snes, &f, &func, &funcctx));
    3380:     PetscCall(VecDuplicate(f, &fpc));
    3381:     PetscCall(SNESSetFunction(snes->npc, fpc, func, funcctx));
    3382:     PetscCall(SNESGetJacobian(snes, &j, &jpre, &jac, &jacctx));
    3383:     PetscCall(SNESSetJacobian(snes->npc, j, jpre, jac, jacctx));
    3384:     PetscCall(SNESGetApplicationContext(snes, &appctx));
    3385:     PetscCall(SNESSetApplicationContext(snes->npc, appctx));
    3386:     PetscCall(SNESSetUseMatrixFree(snes->npc, mf_operator, mf));
    3387:     PetscCall(VecDestroy(&fpc));

    3389:     /* copy the function pointers over */
    3390:     PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)snes, (PetscObject)snes->npc));

    3392:     /* default to 1 iteration */
    3393:     PetscCall(SNESSetTolerances(snes->npc, 0.0, 0.0, 0.0, 1, snes->npc->max_funcs));
    3394:     if (snes->npcside == PC_RIGHT) {
    3395:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_FINAL_ONLY));
    3396:     } else {
    3397:       PetscCall(SNESSetNormSchedule(snes->npc, SNES_NORM_NONE));
    3398:     }
    3399:     PetscCall(SNESSetFromOptions(snes->npc));

    3401:     /* copy the line search context over */
    3402:     if (snes->linesearch && snes->npc->linesearch) {
    3403:       PetscCall(SNESGetLineSearch(snes, &linesearch));
    3404:       PetscCall(SNESGetLineSearch(snes->npc, &pclinesearch));
    3405:       PetscCall(SNESLineSearchGetPreCheck(linesearch, &precheck, &lsprectx));
    3406:       PetscCall(SNESLineSearchGetPostCheck(linesearch, &postcheck, &lspostctx));
    3407:       PetscCall(SNESLineSearchSetPreCheck(pclinesearch, precheck, lsprectx));
    3408:       PetscCall(SNESLineSearchSetPostCheck(pclinesearch, postcheck, lspostctx));
    3409:       PetscCall(PetscObjectCopyFortranFunctionPointers((PetscObject)linesearch, (PetscObject)pclinesearch));
    3410:     }
    3411:   }
    3412:   if (snes->mf) PetscCall(SNESSetUpMatrixFree_Private(snes, snes->mf_operator, snes->mf_version));
    3413:   if (snes->ops->ctxcompute && !snes->ctx) PetscCallBack("SNES callback compute application context", (*snes->ops->ctxcompute)(snes, &snes->ctx));

    3415:   snes->jac_iter = 0;
    3416:   snes->pre_iter = 0;

    3418:   PetscTryTypeMethod(snes, setup);

    3420:   PetscCall(SNESSetDefaultComputeJacobian(snes));

    3422:   if (snes->npc && snes->npcside == PC_LEFT) {
    3423:     if (snes->functype == SNES_FUNCTION_PRECONDITIONED) {
    3424:       if (snes->linesearch) {
    3425:         PetscCall(SNESGetLineSearch(snes, &linesearch));
    3426:         PetscCall(SNESLineSearchSetFunction(linesearch, SNESComputeFunctionDefaultNPC));
    3427:       }
    3428:     }
    3429:   }
    3430:   PetscCall(PetscLogEventEnd(SNES_SetUp, snes, 0, 0, 0));
    3431:   snes->setupcalled = PETSC_TRUE;
    3432:   PetscFunctionReturn(PETSC_SUCCESS);
    3433: }

    3435: /*@
    3436:   SNESReset - Resets a `SNES` context to the state it was in before `SNESSetUp()` was called and removes any allocated `Vec` and `Mat` from its data structures

    3438:   Collective

    3440:   Input Parameter:
    3441: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3443:   Level: intermediate

    3445:   Notes:
    3446:   Any options set on the `SNES` object, including those set with `SNESSetFromOptions()` remain.

    3448:   Call this if you wish to reuse a `SNES` but with different size vectors

    3450:   Also calls the application context destroy routine set with `SNESSetComputeApplicationContext()`

    3452: .seealso: [](ch_snes), `SNES`, `SNESDestroy()`, `SNESCreate()`, `SNESSetUp()`, `SNESSolve()`
    3453: @*/
    3454: PetscErrorCode SNESReset(SNES snes)
    3455: {
    3456:   PetscFunctionBegin;
    3458:   if (snes->ops->ctxdestroy && snes->ctx) {
    3459:     PetscCallBack("SNES callback destroy application context", (*snes->ops->ctxdestroy)(&snes->ctx));
    3460:     snes->ctx = NULL;
    3461:   }
    3462:   if (snes->npc) PetscCall(SNESReset(snes->npc));

    3464:   PetscTryTypeMethod(snes, reset);
    3465:   if (snes->ksp) PetscCall(KSPReset(snes->ksp));

    3467:   if (snes->linesearch) PetscCall(SNESLineSearchReset(snes->linesearch));

    3469:   PetscCall(VecDestroy(&snes->vec_rhs));
    3470:   PetscCall(VecDestroy(&snes->vec_sol));
    3471:   PetscCall(VecDestroy(&snes->vec_sol_update));
    3472:   PetscCall(VecDestroy(&snes->vec_func));
    3473:   PetscCall(MatDestroy(&snes->jacobian));
    3474:   PetscCall(MatDestroy(&snes->jacobian_pre));
    3475:   PetscCall(MatDestroy(&snes->picard));
    3476:   PetscCall(VecDestroyVecs(snes->nwork, &snes->work));
    3477:   PetscCall(VecDestroyVecs(snes->nvwork, &snes->vwork));

    3479:   snes->alwayscomputesfinalresidual = PETSC_FALSE;

    3481:   snes->nwork = snes->nvwork = 0;
    3482:   snes->setupcalled          = PETSC_FALSE;
    3483:   PetscFunctionReturn(PETSC_SUCCESS);
    3484: }

    3486: /*@
    3487:   SNESConvergedReasonViewCancel - Clears all the reason view functions for a `SNES` object provided with `SNESConvergedReasonViewSet()` also
    3488:   removes the default viewer.

    3490:   Collective

    3492:   Input Parameter:
    3493: . snes - the nonlinear iterative solver context obtained from `SNESCreate()`

    3495:   Level: intermediate

    3497: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESReset()`, `SNESConvergedReasonViewSet()`
    3498: @*/
    3499: PetscErrorCode SNESConvergedReasonViewCancel(SNES snes)
    3500: {
    3501:   PetscInt i;

    3503:   PetscFunctionBegin;
    3505:   for (i = 0; i < snes->numberreasonviews; i++) {
    3506:     if (snes->reasonviewdestroy[i]) PetscCall((*snes->reasonviewdestroy[i])(&snes->reasonviewcontext[i]));
    3507:   }
    3508:   snes->numberreasonviews = 0;
    3509:   PetscCall(PetscViewerDestroy(&snes->convergedreasonviewer));
    3510:   PetscFunctionReturn(PETSC_SUCCESS);
    3511: }

    3513: /*@
    3514:   SNESDestroy - Destroys the nonlinear solver context that was created
    3515:   with `SNESCreate()`.

    3517:   Collective

    3519:   Input Parameter:
    3520: . snes - the `SNES` context

    3522:   Level: beginner

    3524: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESSolve()`
    3525: @*/
    3526: PetscErrorCode SNESDestroy(SNES *snes)
    3527: {
    3528:   DM dm;

    3530:   PetscFunctionBegin;
    3531:   if (!*snes) PetscFunctionReturn(PETSC_SUCCESS);
    3533:   if (--((PetscObject)*snes)->refct > 0) {
    3534:     *snes = NULL;
    3535:     PetscFunctionReturn(PETSC_SUCCESS);
    3536:   }

    3538:   PetscCall(SNESReset(*snes));
    3539:   PetscCall(SNESDestroy(&(*snes)->npc));

    3541:   /* if memory was published with SAWs then destroy it */
    3542:   PetscCall(PetscObjectSAWsViewOff((PetscObject)*snes));
    3543:   PetscTryTypeMethod(*snes, destroy);

    3545:   dm = (*snes)->dm;
    3546:   while (dm) {
    3547:     PetscCall(DMCoarsenHookRemove(dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, *snes));
    3548:     PetscCall(DMGetCoarseDM(dm, &dm));
    3549:   }

    3551:   PetscCall(DMDestroy(&(*snes)->dm));
    3552:   PetscCall(KSPDestroy(&(*snes)->ksp));
    3553:   PetscCall(SNESLineSearchDestroy(&(*snes)->linesearch));

    3555:   PetscCall(PetscFree((*snes)->kspconvctx));
    3556:   if ((*snes)->ops->convergeddestroy) PetscCall((*(*snes)->ops->convergeddestroy)(&(*snes)->cnvP));
    3557:   if ((*snes)->conv_hist_alloc) PetscCall(PetscFree2((*snes)->conv_hist, (*snes)->conv_hist_its));
    3558:   PetscCall(SNESMonitorCancel(*snes));
    3559:   PetscCall(SNESConvergedReasonViewCancel(*snes));
    3560:   PetscCall(PetscHeaderDestroy(snes));
    3561:   PetscFunctionReturn(PETSC_SUCCESS);
    3562: }

    3564: /* ----------- Routines to set solver parameters ---------- */

    3566: /*@
    3567:   SNESSetLagPreconditioner - Sets when the preconditioner is rebuilt in the nonlinear solve `SNESSolve()`.

    3569:   Logically Collective

    3571:   Input Parameters:
    3572: + snes - the `SNES` context
    3573: - lag  - 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3574:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3576:   Options Database Keys:
    3577: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple `SNESSolve()`
    3578: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3579: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple `SNESSolve()`
    3580: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3582:   Level: intermediate

    3584:   Notes:
    3585:   The default is 1

    3587:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagPreconditionerPersists()` was called

    3589:   `SNESSetLagPreconditionerPersists()` allows using the same uniform lagging (for example every second linear solve) across multiple nonlinear solves.

    3591: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetLagPreconditionerPersists()`,
    3592:           `SNESSetLagJacobianPersists()`, `SNES`, `SNESSolve()`
    3593: @*/
    3594: PetscErrorCode SNESSetLagPreconditioner(SNES snes, PetscInt lag)
    3595: {
    3596:   PetscFunctionBegin;
    3598:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3599:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3601:   snes->lagpreconditioner = lag;
    3602:   PetscFunctionReturn(PETSC_SUCCESS);
    3603: }

    3605: /*@
    3606:   SNESSetGridSequence - sets the number of steps of grid sequencing that `SNES` will do

    3608:   Logically Collective

    3610:   Input Parameters:
    3611: + snes  - the `SNES` context
    3612: - steps - the number of refinements to do, defaults to 0

    3614:   Options Database Key:
    3615: . -snes_grid_sequence steps - Use grid sequencing to generate initial guess

    3617:   Level: intermediate

    3619:   Notes:
    3620:   Once grid sequencing is turned on `SNESSolve()` will automatically perform the solve on each grid refinement.

    3622:   Use `SNESGetSolution()` to extract the fine grid solution after grid sequencing.

    3624: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetGridSequence()`,
    3625:           `SNESSetDM()`, `SNESSolve()`
    3626: @*/
    3627: PetscErrorCode SNESSetGridSequence(SNES snes, PetscInt steps)
    3628: {
    3629:   PetscFunctionBegin;
    3632:   snes->gridsequence = steps;
    3633:   PetscFunctionReturn(PETSC_SUCCESS);
    3634: }

    3636: /*@
    3637:   SNESGetGridSequence - gets the number of steps of grid sequencing that `SNES` will do

    3639:   Logically Collective

    3641:   Input Parameter:
    3642: . snes - the `SNES` context

    3644:   Output Parameter:
    3645: . steps - the number of refinements to do, defaults to 0

    3647:   Level: intermediate

    3649: .seealso: [](ch_snes), `SNESGetLagPreconditioner()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESSetGridSequence()`
    3650: @*/
    3651: PetscErrorCode SNESGetGridSequence(SNES snes, PetscInt *steps)
    3652: {
    3653:   PetscFunctionBegin;
    3655:   *steps = snes->gridsequence;
    3656:   PetscFunctionReturn(PETSC_SUCCESS);
    3657: }

    3659: /*@
    3660:   SNESGetLagPreconditioner - Return how often the preconditioner is rebuilt

    3662:   Not Collective

    3664:   Input Parameter:
    3665: . snes - the `SNES` context

    3667:   Output Parameter:
    3668: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3669:          the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

    3671:   Level: intermediate

    3673:   Notes:
    3674:   The default is 1

    3676:   The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3678: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3679: @*/
    3680: PetscErrorCode SNESGetLagPreconditioner(SNES snes, PetscInt *lag)
    3681: {
    3682:   PetscFunctionBegin;
    3684:   *lag = snes->lagpreconditioner;
    3685:   PetscFunctionReturn(PETSC_SUCCESS);
    3686: }

    3688: /*@
    3689:   SNESSetLagJacobian - Set when the Jacobian is rebuilt in the nonlinear solve. See `SNESSetLagPreconditioner()` for determining how
    3690:   often the preconditioner is rebuilt.

    3692:   Logically Collective

    3694:   Input Parameters:
    3695: + snes - the `SNES` context
    3696: - lag  - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3697:          the Jacobian is built etc. -2 means rebuild at next chance but then never again

    3699:   Options Database Keys:
    3700: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3701: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3702: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3703: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag.

    3705:   Level: intermediate

    3707:   Notes:
    3708:   The default is 1

    3710:   The Jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

    3712:   If  -1 is used before the very first nonlinear solve the CODE WILL FAIL! because no Jacobian is used, use -2 to indicate you want it recomputed
    3713:   at the next Newton step but never again (unless it is reset to another value)

    3715: .seealso: [](ch_snes), `SNES`, `SNESGetLagPreconditioner()`, `SNESSetLagPreconditioner()`, `SNESGetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3716: @*/
    3717: PetscErrorCode SNESSetLagJacobian(SNES snes, PetscInt lag)
    3718: {
    3719:   PetscFunctionBegin;
    3721:   PetscCheck(lag >= -2, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag must be -2, -1, 1 or greater");
    3722:   PetscCheck(lag, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Lag cannot be 0");
    3724:   snes->lagjacobian = lag;
    3725:   PetscFunctionReturn(PETSC_SUCCESS);
    3726: }

    3728: /*@
    3729:   SNESGetLagJacobian - Get how often the Jacobian is rebuilt. See `SNESGetLagPreconditioner()` to determine when the preconditioner is rebuilt

    3731:   Not Collective

    3733:   Input Parameter:
    3734: . snes - the `SNES` context

    3736:   Output Parameter:
    3737: . lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time
    3738:          the Jacobian is built etc.

    3740:   Level: intermediate

    3742:   Notes:
    3743:   The default is 1

    3745:   The jacobian is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1 or `SNESSetLagJacobianPersists()` was called.

    3747: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobian()`, `SNESSetLagPreconditioner()`, `SNESGetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`
    3748: @*/
    3749: PetscErrorCode SNESGetLagJacobian(SNES snes, PetscInt *lag)
    3750: {
    3751:   PetscFunctionBegin;
    3753:   *lag = snes->lagjacobian;
    3754:   PetscFunctionReturn(PETSC_SUCCESS);
    3755: }

    3757: /*@
    3758:   SNESSetLagJacobianPersists - Set whether or not the Jacobian lagging persists through multiple nonlinear solves

    3760:   Logically collective

    3762:   Input Parameters:
    3763: + snes - the `SNES` context
    3764: - flg  - jacobian lagging persists if true

    3766:   Options Database Keys:
    3767: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3768: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3769: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3770: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3772:   Level: advanced

    3774:   Notes:
    3775:   Normally when `SNESSetLagJacobian()` is used, the Jacobian is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3777:   This is useful both for nonlinear preconditioning, where it's appropriate to have the Jacobian be stale by
    3778:   several solves, and for implicit time-stepping, where Jacobian lagging in the inner nonlinear solve over several
    3779:   timesteps may present huge efficiency gains.

    3781: .seealso: [](ch_snes), `SNES`, `SNESSetLagPreconditionerPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`
    3782: @*/
    3783: PetscErrorCode SNESSetLagJacobianPersists(SNES snes, PetscBool flg)
    3784: {
    3785:   PetscFunctionBegin;
    3788:   snes->lagjac_persist = flg;
    3789:   PetscFunctionReturn(PETSC_SUCCESS);
    3790: }

    3792: /*@
    3793:   SNESSetLagPreconditionerPersists - Set whether or not the preconditioner lagging persists through multiple nonlinear solves

    3795:   Logically Collective

    3797:   Input Parameters:
    3798: + snes - the `SNES` context
    3799: - flg  - preconditioner lagging persists if true

    3801:   Options Database Keys:
    3802: + -snes_lag_jacobian_persists (true|false)       - sets the persistence through multiple SNES solves
    3803: . -snes_lag_jacobian (-2|1|2|...)                - sets the lag
    3804: . -snes_lag_preconditioner_persists (true|false) - sets the persistence through multiple SNES solves
    3805: - -snes_lag_preconditioner (-2|1|2|...)          - sets the lag

    3807:   Level: developer

    3809:   Notes:
    3810:   Normally when `SNESSetLagPreconditioner()` is used, the preconditioner is always rebuilt at the beginning of each new nonlinear solve, this removes that behavior

    3812:   This is useful both for nonlinear preconditioning, where it's appropriate to have the preconditioner be stale
    3813:   by several solves, and for implicit time-stepping, where preconditioner lagging in the inner nonlinear solve over
    3814:   several timesteps may present huge efficiency gains.

    3816: .seealso: [](ch_snes), `SNES`, `SNESSetLagJacobianPersists()`, `SNESSetLagJacobian()`, `SNESGetLagJacobian()`, `SNESGetNPC()`, `SNESSetLagPreconditioner()`
    3817: @*/
    3818: PetscErrorCode SNESSetLagPreconditionerPersists(SNES snes, PetscBool flg)
    3819: {
    3820:   PetscFunctionBegin;
    3823:   snes->lagpre_persist = flg;
    3824:   PetscFunctionReturn(PETSC_SUCCESS);
    3825: }

    3827: /*@
    3828:   SNESSetForceIteration - force `SNESSolve()` to take at least one iteration regardless of the initial residual norm

    3830:   Logically Collective

    3832:   Input Parameters:
    3833: + snes  - the `SNES` context
    3834: - force - `PETSC_TRUE` require at least one iteration

    3836:   Options Database Key:
    3837: . -snes_force_iteration force - Sets forcing an iteration

    3839:   Level: intermediate

    3841:   Note:
    3842:   This is used sometimes with `TS` to prevent `TS` from detecting a false steady state solution

    3844: .seealso: [](ch_snes), `SNES`, `TS`, `SNESSetDivergenceTolerance()`
    3845: @*/
    3846: PetscErrorCode SNESSetForceIteration(SNES snes, PetscBool force)
    3847: {
    3848:   PetscFunctionBegin;
    3850:   snes->forceiteration = force;
    3851:   PetscFunctionReturn(PETSC_SUCCESS);
    3852: }

    3854: /*@
    3855:   SNESGetForceIteration - Check whether or not `SNESSolve()` take at least one iteration regardless of the initial residual norm

    3857:   Logically Collective

    3859:   Input Parameter:
    3860: . snes - the `SNES` context

    3862:   Output Parameter:
    3863: . force - `PETSC_TRUE` requires at least one iteration.

    3865:   Level: intermediate

    3867: .seealso: [](ch_snes), `SNES`, `SNESSetForceIteration()`, `SNESSetDivergenceTolerance()`
    3868: @*/
    3869: PetscErrorCode SNESGetForceIteration(SNES snes, PetscBool *force)
    3870: {
    3871:   PetscFunctionBegin;
    3873:   *force = snes->forceiteration;
    3874:   PetscFunctionReturn(PETSC_SUCCESS);
    3875: }

    3877: /*@
    3878:   SNESSetTolerances - Sets various parameters used in `SNES` convergence tests.

    3880:   Logically Collective

    3882:   Input Parameters:
    3883: + snes   - the `SNES` context
    3884: . abstol - the absolute convergence tolerance, $ F(x^n) \le abstol $
    3885: . rtol   - the relative convergence tolerance, $ F(x^n) \le reltol * F(x^0) $
    3886: . stol   - convergence tolerance in terms of the norm of the change in the solution between steps,  || delta x || < stol*|| x ||
    3887: . maxit  - the maximum number of iterations allowed in the solver, default 50.
    3888: - maxf   - the maximum number of function evaluations allowed in the solver (use `PETSC_UNLIMITED` indicates no limit), default 10,000

    3890:   Options Database Keys:
    3891: + -snes_atol abstol    - Sets `abstol`
    3892: . -snes_rtol rtol      - Sets `rtol`
    3893: . -snes_stol stol      - Sets `stol`
    3894: . -snes_max_it maxit   - Sets `maxit`
    3895: - -snes_max_funcs maxf - Sets `maxf` (use `unlimited` to have no maximum)

    3897:   Level: intermediate

    3899:   Note:
    3900:   All parameters must be non-negative

    3902:   Use `PETSC_CURRENT` to retain the current value of any parameter and `PETSC_DETERMINE` to use the default value for the given `SNES`.
    3903:   The default value is the value in the object when its type is set.

    3905:   Use `PETSC_UNLIMITED` on `maxit` or `maxf` to indicate there is no bound on the number of iterations or number of function evaluations.

    3907:   Fortran Note:
    3908:   Use `PETSC_CURRENT_INTEGER`, `PETSC_CURRENT_REAL`, `PETSC_UNLIMITED_INTEGER`, `PETSC_DETERMINE_INTEGER`, or `PETSC_DETERMINE_REAL`

    3910: .seealso: [](ch_snes), `SNESSolve()`, `SNES`, `SNESSetDivergenceTolerance()`, `SNESSetForceIteration()`
    3911: @*/
    3912: PetscErrorCode SNESSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit, PetscInt maxf)
    3913: {
    3914:   PetscFunctionBegin;

    3922:   if (abstol == (PetscReal)PETSC_DETERMINE) {
    3923:     snes->abstol = snes->default_abstol;
    3924:   } else if (abstol != (PetscReal)PETSC_CURRENT) {
    3925:     PetscCheck(abstol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Absolute tolerance %g must be non-negative", (double)abstol);
    3926:     snes->abstol = abstol;
    3927:   }

    3929:   if (rtol == (PetscReal)PETSC_DETERMINE) {
    3930:     snes->rtol = snes->default_rtol;
    3931:   } else if (rtol != (PetscReal)PETSC_CURRENT) {
    3932:     PetscCheck(rtol >= 0.0 && 1.0 > rtol, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Relative tolerance %g must be non-negative and less than 1.0", (double)rtol);
    3933:     snes->rtol = rtol;
    3934:   }

    3936:   if (stol == (PetscReal)PETSC_DETERMINE) {
    3937:     snes->stol = snes->default_stol;
    3938:   } else if (stol != (PetscReal)PETSC_CURRENT) {
    3939:     PetscCheck(stol >= 0.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Step tolerance %g must be non-negative", (double)stol);
    3940:     snes->stol = stol;
    3941:   }

    3943:   if (maxit == PETSC_DETERMINE) {
    3944:     snes->max_its = snes->default_max_its;
    3945:   } else if (maxit == PETSC_UNLIMITED) {
    3946:     snes->max_its = PETSC_INT_MAX;
    3947:   } else if (maxit != PETSC_CURRENT) {
    3948:     PetscCheck(maxit >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of iterations %" PetscInt_FMT " must be non-negative", maxit);
    3949:     snes->max_its = maxit;
    3950:   }

    3952:   if (maxf == PETSC_DETERMINE) {
    3953:     snes->max_funcs = snes->default_max_funcs;
    3954:   } else if (maxf == PETSC_UNLIMITED || maxf == -1) {
    3955:     snes->max_funcs = PETSC_UNLIMITED;
    3956:   } else if (maxf != PETSC_CURRENT) {
    3957:     PetscCheck(maxf >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Maximum number of function evaluations %" PetscInt_FMT " must be nonnegative", maxf);
    3958:     snes->max_funcs = maxf;
    3959:   }
    3960:   PetscFunctionReturn(PETSC_SUCCESS);
    3961: }

    3963: /*@
    3964:   SNESSetDivergenceTolerance - Sets the divergence tolerance used for the `SNES` divergence test.

    3966:   Logically Collective

    3968:   Input Parameters:
    3969: + snes   - the `SNES` context
    3970: - divtol - the divergence tolerance. Use `PETSC_UNLIMITED` to deactivate the test. If the residual norm $ F(x^n) \ge divtol * F(x^0) $ the solver
    3971:            is stopped due to divergence.

    3973:   Options Database Key:
    3974: . -snes_divergence_tolerance divtol - Sets `divtol`

    3976:   Level: intermediate

    3978:   Notes:
    3979:   Use `PETSC_DETERMINE` to use the default value from when the object's type was set.

    3981:   Fortran Note:
    3982:   Use ``PETSC_DETERMINE_REAL` or `PETSC_UNLIMITED_REAL`

    3984: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetTolerances()`, `SNESGetDivergenceTolerance()`
    3985: @*/
    3986: PetscErrorCode SNESSetDivergenceTolerance(SNES snes, PetscReal divtol)
    3987: {
    3988:   PetscFunctionBegin;

    3992:   if (divtol == (PetscReal)PETSC_DETERMINE) {
    3993:     snes->divtol = snes->default_divtol;
    3994:   } else if (divtol == (PetscReal)PETSC_UNLIMITED || divtol == -1) {
    3995:     snes->divtol = PETSC_UNLIMITED;
    3996:   } else if (divtol != (PetscReal)PETSC_CURRENT) {
    3997:     PetscCheck(divtol >= 1.0, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_OUTOFRANGE, "Divergence tolerance %g must be greater than 1.0", (double)divtol);
    3998:     snes->divtol = divtol;
    3999:   }
    4000:   PetscFunctionReturn(PETSC_SUCCESS);
    4001: }

    4003: /*@
    4004:   SNESGetTolerances - Gets various parameters used in `SNES` convergence tests.

    4006:   Not Collective

    4008:   Input Parameter:
    4009: . snes - the `SNES` context

    4011:   Output Parameters:
    4012: + atol  - the absolute convergence tolerance
    4013: . rtol  - the relative convergence tolerance
    4014: . stol  - convergence tolerance in terms of the norm of the change in the solution between steps
    4015: . maxit - the maximum number of iterations allowed
    4016: - maxf  - the maximum number of function evaluations allowed, `PETSC_UNLIMITED` indicates no bound

    4018:   Level: intermediate

    4020:   Notes:
    4021:   See `SNESSetTolerances()` for details on the parameters.

    4023:   The user can specify `NULL` for any parameter that is not needed.

    4025: .seealso: [](ch_snes), `SNES`, `SNESSetTolerances()`
    4026: @*/
    4027: PetscErrorCode SNESGetTolerances(SNES snes, PetscReal *atol, PetscReal *rtol, PetscReal *stol, PetscInt *maxit, PetscInt *maxf)
    4028: {
    4029:   PetscFunctionBegin;
    4031:   if (atol) *atol = snes->abstol;
    4032:   if (rtol) *rtol = snes->rtol;
    4033:   if (stol) *stol = snes->stol;
    4034:   if (maxit) *maxit = snes->max_its;
    4035:   if (maxf) *maxf = snes->max_funcs;
    4036:   PetscFunctionReturn(PETSC_SUCCESS);
    4037: }

    4039: /*@
    4040:   SNESGetDivergenceTolerance - Gets divergence tolerance used in divergence test.

    4042:   Not Collective

    4044:   Input Parameters:
    4045: + snes   - the `SNES` context
    4046: - divtol - divergence tolerance

    4048:   Level: intermediate

    4050: .seealso: [](ch_snes), `SNES`, `SNESSetDivergenceTolerance()`
    4051: @*/
    4052: PetscErrorCode SNESGetDivergenceTolerance(SNES snes, PetscReal *divtol)
    4053: {
    4054:   PetscFunctionBegin;
    4056:   if (divtol) *divtol = snes->divtol;
    4057:   PetscFunctionReturn(PETSC_SUCCESS);
    4058: }

    4060: PETSC_INTERN PetscErrorCode SNESMonitorRange_Private(SNES, PetscInt, PetscReal *);

    4062: PetscErrorCode SNESMonitorLGRange(SNES snes, PetscInt n, PetscReal rnorm, PetscCtx monctx)
    4063: {
    4064:   PetscDrawLG      lg;
    4065:   PetscReal        x, y, per;
    4066:   PetscViewer      v = (PetscViewer)monctx;
    4067:   static PetscReal prev; /* should be in the context */
    4068:   PetscDraw        draw;

    4070:   PetscFunctionBegin;
    4072:   PetscCall(PetscViewerDrawGetDrawLG(v, 0, &lg));
    4073:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4074:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4075:   PetscCall(PetscDrawSetTitle(draw, "Residual norm"));
    4076:   x = (PetscReal)n;
    4077:   if (rnorm > 0.0) y = PetscLog10Real(rnorm);
    4078:   else y = -15.0;
    4079:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4080:   if (n < 20 || !(n % 5) || snes->reason) {
    4081:     PetscCall(PetscDrawLGDraw(lg));
    4082:     PetscCall(PetscDrawLGSave(lg));
    4083:   }

    4085:   PetscCall(PetscViewerDrawGetDrawLG(v, 1, &lg));
    4086:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4087:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4088:   PetscCall(PetscDrawSetTitle(draw, "% elements > .2*max element"));
    4089:   PetscCall(SNESMonitorRange_Private(snes, n, &per));
    4090:   x = (PetscReal)n;
    4091:   y = 100.0 * per;
    4092:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4093:   if (n < 20 || !(n % 5) || snes->reason) {
    4094:     PetscCall(PetscDrawLGDraw(lg));
    4095:     PetscCall(PetscDrawLGSave(lg));
    4096:   }

    4098:   PetscCall(PetscViewerDrawGetDrawLG(v, 2, &lg));
    4099:   if (!n) {
    4100:     prev = rnorm;
    4101:     PetscCall(PetscDrawLGReset(lg));
    4102:   }
    4103:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4104:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm"));
    4105:   x = (PetscReal)n;
    4106:   y = (prev - rnorm) / prev;
    4107:   PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4108:   if (n < 20 || !(n % 5) || snes->reason) {
    4109:     PetscCall(PetscDrawLGDraw(lg));
    4110:     PetscCall(PetscDrawLGSave(lg));
    4111:   }

    4113:   PetscCall(PetscViewerDrawGetDrawLG(v, 3, &lg));
    4114:   if (!n) PetscCall(PetscDrawLGReset(lg));
    4115:   PetscCall(PetscDrawLGGetDraw(lg, &draw));
    4116:   PetscCall(PetscDrawSetTitle(draw, "(norm -oldnorm)/oldnorm*(% > .2 max)"));
    4117:   x = (PetscReal)n;
    4118:   y = (prev - rnorm) / (prev * per);
    4119:   if (n > 2) { /*skip initial crazy value */
    4120:     PetscCall(PetscDrawLGAddPoint(lg, &x, &y));
    4121:   }
    4122:   if (n < 20 || !(n % 5) || snes->reason) {
    4123:     PetscCall(PetscDrawLGDraw(lg));
    4124:     PetscCall(PetscDrawLGSave(lg));
    4125:   }
    4126:   prev = rnorm;
    4127:   PetscFunctionReturn(PETSC_SUCCESS);
    4128: }

    4130: /*@
    4131:   SNESConverged - Run the convergence test and update the `SNESConvergedReason`.

    4133:   Collective

    4135:   Input Parameters:
    4136: + snes  - the `SNES` context
    4137: . it    - current iteration
    4138: . xnorm - 2-norm of current iterate
    4139: . snorm - 2-norm of current step
    4140: - fnorm - 2-norm of function

    4142:   Level: developer

    4144:   Note:
    4145:   This routine is called by the `SNESSolve()` implementations.
    4146:   It does not typically need to be called by the user.

    4148: .seealso: [](ch_snes), `SNES`, `SNESSolve`, `SNESSetConvergenceTest()`
    4149: @*/
    4150: PetscErrorCode SNESConverged(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm)
    4151: {
    4152:   PetscFunctionBegin;
    4153:   if (!snes->reason) {
    4154:     if (snes->normschedule == SNES_NORM_ALWAYS) PetscUseTypeMethod(snes, converged, it, xnorm, snorm, fnorm, &snes->reason, snes->cnvP);
    4155:     if (it == snes->max_its && !snes->reason) {
    4156:       if (snes->normschedule == SNES_NORM_ALWAYS) {
    4157:         PetscCall(PetscInfo(snes, "Maximum number of iterations has been reached: %" PetscInt_FMT "\n", snes->max_its));
    4158:         snes->reason = SNES_DIVERGED_MAX_IT;
    4159:       } else snes->reason = SNES_CONVERGED_ITS;
    4160:     }
    4161:   }
    4162:   PetscFunctionReturn(PETSC_SUCCESS);
    4163: }

    4165: /*@
    4166:   SNESMonitor - runs any `SNES` monitor routines provided with `SNESMonitor()` or the options database

    4168:   Collective

    4170:   Input Parameters:
    4171: + snes  - nonlinear solver context obtained from `SNESCreate()`
    4172: . iter  - current iteration number
    4173: - rnorm - current relative norm of the residual

    4175:   Level: developer

    4177:   Note:
    4178:   This routine is called by the `SNESSolve()` implementations.
    4179:   It does not typically need to be called by the user.

    4181: .seealso: [](ch_snes), `SNES`, `SNESMonitorSet()`
    4182: @*/
    4183: PetscErrorCode SNESMonitor(SNES snes, PetscInt iter, PetscReal rnorm)
    4184: {
    4185:   PetscInt i, n = snes->numbermonitors;

    4187:   PetscFunctionBegin;
    4188:   PetscCall(VecLockReadPush(snes->vec_sol));
    4189:   for (i = 0; i < n; i++) PetscCall((*snes->monitor[i])(snes, iter, rnorm, snes->monitorcontext[i]));
    4190:   PetscCall(VecLockReadPop(snes->vec_sol));
    4191:   PetscFunctionReturn(PETSC_SUCCESS);
    4192: }

    4194: /* ------------ Routines to set performance monitoring options ----------- */

    4196: /*MC
    4197:     SNESMonitorFunction - functional form passed to `SNESMonitorSet()` to monitor convergence of nonlinear solver

    4199:      Synopsis:
    4200: #include <petscsnes.h>
    4201:     PetscErrorCode SNESMonitorFunction(SNES snes, PetscInt its, PetscReal norm, PetscCtx mctx)

    4203:      Collective

    4205:     Input Parameters:
    4206: +    snes - the `SNES` context
    4207: .    its - iteration number
    4208: .    norm - 2-norm function value (may be estimated)
    4209: -    mctx - [optional] monitoring context

    4211:    Level: advanced

    4213: .seealso: [](ch_snes), `SNESMonitorSet()`, `PetscCtx`
    4214: M*/

    4216: /*@C
    4217:   SNESMonitorSet - Sets an ADDITIONAL function that is to be used at every
    4218:   iteration of the `SNES` nonlinear solver to display the iteration's
    4219:   progress.

    4221:   Logically Collective

    4223:   Input Parameters:
    4224: + snes           - the `SNES` context
    4225: . f              - the monitor function,  for the calling sequence see `SNESMonitorFunction`
    4226: . mctx           - [optional] user-defined context for private data for the monitor routine (use `NULL` if no context is desired)
    4227: - monitordestroy - [optional] routine that frees monitor context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4229:   Calling sequence of f:
    4230: + snes  - the `SNES` object
    4231: . it    - the current iteration
    4232: . rnorm - norm of the residual
    4233: - mctx  - the optional monitor context

    4235:   Options Database Keys:
    4236: + -snes_monitor               - sets `SNESMonitorDefault()`
    4237: . -snes_monitor draw::draw_lg - sets line graph monitor,
    4238: - -snes_monitor_cancel        - cancels all monitors that have been hardwired into a code by calls to `SNESMonitorSet()`, but does not cancel those set via
    4239:                                 the options database.

    4241:   Level: intermediate

    4243:   Note:
    4244:   Several different monitoring routines may be set by calling
    4245:   `SNESMonitorSet()` multiple times; all will be called in the
    4246:   order in which they were set.

    4248:   Fortran Note:
    4249:   Only a single monitor function can be set for each `SNES` object

    4251: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESMonitorDefault()`, `SNESMonitorCancel()`, `SNESMonitorFunction`, `PetscCtxDestroyFn`
    4252: @*/
    4253: PetscErrorCode SNESMonitorSet(SNES snes, PetscErrorCode (*f)(SNES snes, PetscInt it, PetscReal rnorm, PetscCtx mctx), PetscCtx mctx, PetscCtxDestroyFn *monitordestroy)
    4254: {
    4255:   PetscFunctionBegin;
    4257:   for (PetscInt i = 0; i < snes->numbermonitors; i++) {
    4258:     PetscBool identical;

    4260:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, mctx, monitordestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->monitor[i], snes->monitorcontext[i], snes->monitordestroy[i], &identical));
    4261:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4262:   }
    4263:   PetscCheck(snes->numbermonitors < MAXSNESMONITORS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many monitors set");
    4264:   snes->monitor[snes->numbermonitors]          = f;
    4265:   snes->monitordestroy[snes->numbermonitors]   = monitordestroy;
    4266:   snes->monitorcontext[snes->numbermonitors++] = mctx;
    4267:   PetscFunctionReturn(PETSC_SUCCESS);
    4268: }

    4270: /*@
    4271:   SNESMonitorCancel - Clears all the monitor functions for a `SNES` object.

    4273:   Logically Collective

    4275:   Input Parameter:
    4276: . snes - the `SNES` context

    4278:   Options Database Key:
    4279: . -snes_monitor_cancel - cancels all monitors that have been hardwired
    4280:                          into a code by calls to `SNESMonitorSet()`, but does not cancel those
    4281:                          set via the options database

    4283:   Level: intermediate

    4285:   Note:
    4286:   There is no way to clear one specific monitor from a `SNES` object.

    4288: .seealso: [](ch_snes), `SNES`, `SNESMonitorDefault()`, `SNESMonitorSet()`
    4289: @*/
    4290: PetscErrorCode SNESMonitorCancel(SNES snes)
    4291: {
    4292:   PetscInt i;

    4294:   PetscFunctionBegin;
    4296:   for (i = 0; i < snes->numbermonitors; i++) {
    4297:     if (snes->monitordestroy[i]) PetscCall((*snes->monitordestroy[i])(&snes->monitorcontext[i]));
    4298:   }
    4299:   snes->numbermonitors = 0;
    4300:   PetscFunctionReturn(PETSC_SUCCESS);
    4301: }

    4303: /*@C
    4304:   SNESSetConvergenceTest - Sets the function that is to be used
    4305:   to test for convergence of the nonlinear iterative solution.

    4307:   Logically Collective

    4309:   Input Parameters:
    4310: + snes    - the `SNES` context
    4311: . func    - routine to test for convergence
    4312: . ctx     - [optional] context for private data for the convergence routine  (may be `NULL`)
    4313: - destroy - [optional] destructor for the context (may be `NULL`; `PETSC_NULL_FUNCTION` in Fortran)

    4315:   Calling sequence of func:
    4316: + snes   - the `SNES` context
    4317: . it     - the current iteration number
    4318: . xnorm  - the norm of the new solution
    4319: . snorm  - the norm of the step
    4320: . fnorm  - the norm of the function value
    4321: . reason - output, the reason convergence or divergence as declared
    4322: - ctx    - the optional convergence test context

    4324:   Level: advanced

    4326: .seealso: [](ch_snes), `SNES`, `SNESConvergedDefault()`, `SNESConvergedSkip()`
    4327: @*/
    4328: PetscErrorCode SNESSetConvergenceTest(SNES snes, PetscErrorCode (*func)(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm, SNESConvergedReason *reason, PetscCtx ctx), PetscCtx ctx, PetscCtxDestroyFn *destroy)
    4329: {
    4330:   PetscFunctionBegin;
    4332:   if (!func) func = SNESConvergedSkip;
    4333:   if (snes->ops->convergeddestroy) PetscCall((*snes->ops->convergeddestroy)(&snes->cnvP));
    4334:   snes->ops->converged        = func;
    4335:   snes->ops->convergeddestroy = destroy;
    4336:   snes->cnvP                  = ctx;
    4337:   PetscFunctionReturn(PETSC_SUCCESS);
    4338: }

    4340: /*@
    4341:   SNESGetConvergedReason - Gets the reason the `SNES` iteration was stopped, which may be due to convergence, divergence, or stagnation

    4343:   Not Collective

    4345:   Input Parameter:
    4346: . snes - the `SNES` context

    4348:   Output Parameter:
    4349: . reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` for the individual convergence tests for complete lists

    4351:   Options Database Key:
    4352: . -snes_converged_reason - prints the reason to standard out

    4354:   Level: intermediate

    4356:   Note:
    4357:   Should only be called after the call the `SNESSolve()` is complete, if it is called earlier it returns the value `SNES__CONVERGED_ITERATING`.

    4359: .seealso: [](ch_snes), `SNESSolve()`, `SNESSetConvergenceTest()`, `SNESSetConvergedReason()`, `SNESConvergedReason`, `SNESGetConvergedReasonString()`
    4360: @*/
    4361: PetscErrorCode SNESGetConvergedReason(SNES snes, SNESConvergedReason *reason)
    4362: {
    4363:   PetscFunctionBegin;
    4365:   PetscAssertPointer(reason, 2);
    4366:   *reason = snes->reason;
    4367:   PetscFunctionReturn(PETSC_SUCCESS);
    4368: }

    4370: /*@C
    4371:   SNESGetConvergedReasonString - Return a human readable string for `SNESConvergedReason`

    4373:   Not Collective

    4375:   Input Parameter:
    4376: . snes - the `SNES` context

    4378:   Output Parameter:
    4379: . strreason - a human readable string that describes `SNES` converged reason

    4381:   Level: beginner

    4383: .seealso: [](ch_snes), `SNES`, `SNESGetConvergedReason()`
    4384: @*/
    4385: PetscErrorCode SNESGetConvergedReasonString(SNES snes, const char **strreason)
    4386: {
    4387:   PetscFunctionBegin;
    4389:   PetscAssertPointer(strreason, 2);
    4390:   *strreason = SNESConvergedReasons[snes->reason];
    4391:   PetscFunctionReturn(PETSC_SUCCESS);
    4392: }

    4394: /*@
    4395:   SNESSetConvergedReason - Sets the reason the `SNES` iteration was stopped.

    4397:   Not Collective

    4399:   Input Parameters:
    4400: + snes   - the `SNES` context
    4401: - reason - negative value indicates diverged, positive value converged, see `SNESConvergedReason` or the
    4402:             manual pages for the individual convergence tests for complete lists

    4404:   Level: developer

    4406:   Developer Note:
    4407:   Called inside the various `SNESSolve()` implementations

    4409: .seealso: [](ch_snes), `SNESGetConvergedReason()`, `SNESSetConvergenceTest()`, `SNESConvergedReason`
    4410: @*/
    4411: PetscErrorCode SNESSetConvergedReason(SNES snes, SNESConvergedReason reason)
    4412: {
    4413:   PetscFunctionBegin;
    4415:   PetscCheck(!snes->errorifnotconverged || reason > 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_PLIB, "SNES code should have previously errored due to negative reason");
    4416:   snes->reason = reason;
    4417:   PetscFunctionReturn(PETSC_SUCCESS);
    4418: }

    4420: /*@
    4421:   SNESSetConvergenceHistory - Sets the arrays used to hold the convergence history.

    4423:   Logically Collective

    4425:   Input Parameters:
    4426: + snes  - iterative context obtained from `SNESCreate()`
    4427: . a     - array to hold history, this array will contain the function norms computed at each step
    4428: . its   - integer array holds the number of linear iterations for each solve.
    4429: . na    - size of `a` and `its`
    4430: - reset - `PETSC_TRUE` indicates each new nonlinear solve resets the history counter to zero,
    4431:           else it continues storing new values for new nonlinear solves after the old ones

    4433:   Level: intermediate

    4435:   Notes:
    4436:   If 'a' and 'its' are `NULL` then space is allocated for the history. If 'na' is `PETSC_DECIDE` (or, deprecated, `PETSC_DEFAULT`) then a
    4437:   default array of length 1,000 is allocated.

    4439:   This routine is useful, e.g., when running a code for purposes
    4440:   of accurate performance monitoring, when no I/O should be done
    4441:   during the section of code that is being timed.

    4443:   If the arrays run out of space after a number of iterations then the later values are not saved in the history

    4445: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetConvergenceHistory()`
    4446: @*/
    4447: PetscErrorCode SNESSetConvergenceHistory(SNES snes, PetscReal a[], PetscInt its[], PetscInt na, PetscBool reset)
    4448: {
    4449:   PetscFunctionBegin;
    4451:   if (a) PetscAssertPointer(a, 2);
    4452:   if (its) PetscAssertPointer(its, 3);
    4453:   if (!a) {
    4454:     if (na == PETSC_DECIDE) na = 1000;
    4455:     PetscCall(PetscCalloc2(na, &a, na, &its));
    4456:     snes->conv_hist_alloc = PETSC_TRUE;
    4457:   }
    4458:   snes->conv_hist       = a;
    4459:   snes->conv_hist_its   = its;
    4460:   snes->conv_hist_max   = (size_t)na;
    4461:   snes->conv_hist_len   = 0;
    4462:   snes->conv_hist_reset = reset;
    4463:   PetscFunctionReturn(PETSC_SUCCESS);
    4464: }

    4466: #if defined(PETSC_HAVE_MATLAB)
    4467:   #include <engine.h> /* MATLAB include file */
    4468:   #include <mex.h>    /* MATLAB include file */

    4470: PETSC_EXTERN mxArray *SNESGetConvergenceHistoryMatlab(SNES snes)
    4471: {
    4472:   mxArray   *mat;
    4473:   PetscInt   i;
    4474:   PetscReal *ar;

    4476:   mat = mxCreateDoubleMatrix(snes->conv_hist_len, 1, mxREAL);
    4477:   ar  = (PetscReal *)mxGetData(mat);
    4478:   for (i = 0; i < snes->conv_hist_len; i++) ar[i] = snes->conv_hist[i];
    4479:   return mat;
    4480: }
    4481: #endif

    4483: /*@C
    4484:   SNESGetConvergenceHistory - Gets the arrays used to hold the convergence history.

    4486:   Not Collective

    4488:   Input Parameter:
    4489: . snes - iterative context obtained from `SNESCreate()`

    4491:   Output Parameters:
    4492: + a   - array to hold history, usually was set with `SNESSetConvergenceHistory()`
    4493: . its - integer array holds the number of linear iterations (or
    4494:          negative if not converged) for each solve.
    4495: - na  - size of `a` and `its`

    4497:   Level: intermediate

    4499:   Note:
    4500:   This routine is useful, e.g., when running a code for purposes
    4501:   of accurate performance monitoring, when no I/O should be done
    4502:   during the section of code that is being timed.

    4504:   Fortran Notes:
    4505:   Return the arrays with ``SNESRestoreConvergenceHistory()`

    4507:   Use the arguments
    4508: .vb
    4509:   PetscReal, pointer :: a(:)
    4510:   PetscInt, pointer :: its(:)
    4511: .ve

    4513: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetConvergenceHistory()`
    4514: @*/
    4515: PetscErrorCode SNESGetConvergenceHistory(SNES snes, PetscReal *a[], PetscInt *its[], PetscInt *na)
    4516: {
    4517:   PetscFunctionBegin;
    4519:   if (a) *a = snes->conv_hist;
    4520:   if (its) *its = snes->conv_hist_its;
    4521:   if (na) *na = (PetscInt)snes->conv_hist_len;
    4522:   PetscFunctionReturn(PETSC_SUCCESS);
    4523: }

    4525: /*@C
    4526:   SNESSetUpdate - Sets the general-purpose update function called
    4527:   at the beginning of every iteration of the nonlinear solve. Specifically
    4528:   it is called just before the Jacobian is "evaluated" and after the function
    4529:   evaluation.

    4531:   Logically Collective

    4533:   Input Parameters:
    4534: + snes - The nonlinear solver context
    4535: - func - The update function; for calling sequence see `SNESUpdateFn`

    4537:   Level: advanced

    4539:   Notes:
    4540:   This is NOT what one uses to update the ghost points before a function evaluation, that should be done at the beginning of your function provided
    4541:   to `SNESSetFunction()`, or `SNESSetPicard()`
    4542:   This is not used by most users, and it is intended to provide a general hook that is run
    4543:   right before the direction step is computed.

    4545:   Users are free to modify the current residual vector,
    4546:   the current linearization point, or any other vector associated to the specific solver used.
    4547:   If such modifications take place, it is the user responsibility to update all the relevant
    4548:   vectors. For example, if one is adjusting the model parameters at each Newton step their code may look like
    4549: .vb
    4550:   PetscErrorCode update(SNES snes, PetscInt iteration)
    4551:   {
    4552:     PetscFunctionBeginUser;
    4553:     if (iteration > 0) {
    4554:       // update the model parameters here
    4555:       Vec x,f;
    4556:       PetscCall(SNESGetSolution(snes,&x));
    4557:       PetcCall(SNESGetFunction(snes,&f,NULL,NULL));
    4558:       PetscCall(SNESComputeFunction(snes,x,f));
    4559:     }
    4560:     PetscFunctionReturn(PETSC_SUCCESS);
    4561:   }
    4562: .ve

    4564:   There are a variety of function hooks one many set that are called at different stages of the nonlinear solution process, see the functions listed below.

    4566: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetJacobian()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchSetPostCheck()`, `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRSetPostCheck()`,
    4567:          `SNESMonitorSet()`
    4568: @*/
    4569: PetscErrorCode SNESSetUpdate(SNES snes, SNESUpdateFn *func)
    4570: {
    4571:   PetscFunctionBegin;
    4573:   snes->ops->update = func;
    4574:   PetscFunctionReturn(PETSC_SUCCESS);
    4575: }

    4577: /*@
    4578:   SNESConvergedReasonView - Displays the reason a `SNES` solve converged or diverged to a viewer

    4580:   Collective

    4582:   Input Parameters:
    4583: + snes   - iterative context obtained from `SNESCreate()`
    4584: - viewer - the viewer to display the reason

    4586:   Options Database Keys:
    4587: + -snes_converged_reason          - print reason for converged or diverged, also prints number of iterations
    4588: - -snes_converged_reason ::failed - only print reason and number of iterations when diverged

    4590:   Level: beginner

    4592:   Note:
    4593:   To change the format of the output call `PetscViewerPushFormat`(viewer,format) before this call. Use `PETSC_VIEWER_DEFAULT` for the default,
    4594:   use `PETSC_VIEWER_FAILED` to only display a reason if it fails.

    4596: .seealso: [](ch_snes), `SNESConvergedReason`, `PetscViewer`, `SNES`,
    4597:           `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`, `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`,
    4598:           `SNESConvergedReasonViewFromOptions()`,
    4599:           `PetscViewerPushFormat()`, `PetscViewerPopFormat()`
    4600: @*/
    4601: PetscErrorCode SNESConvergedReasonView(SNES snes, PetscViewer viewer)
    4602: {
    4603:   PetscViewerFormat format;
    4604:   PetscBool         isAscii;

    4606:   PetscFunctionBegin;
    4607:   if (!viewer) viewer = PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes));
    4608:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &isAscii));
    4609:   if (isAscii) {
    4610:     PetscCall(PetscViewerGetFormat(viewer, &format));
    4611:     PetscCall(PetscViewerASCIIAddTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4612:     if (format == PETSC_VIEWER_ASCII_INFO_DETAIL) {
    4613:       DM       dm;
    4614:       Vec      u;
    4615:       PetscDS  prob;
    4616:       PetscInt Nf, f;
    4617:       PetscErrorCode (**exactSol)(PetscInt, PetscReal, const PetscReal[], PetscInt, PetscScalar[], void *);
    4618:       void    **exactCtx;
    4619:       PetscReal error;

    4621:       PetscCall(SNESGetDM(snes, &dm));
    4622:       PetscCall(SNESGetSolution(snes, &u));
    4623:       PetscCall(DMGetDS(dm, &prob));
    4624:       PetscCall(PetscDSGetNumFields(prob, &Nf));
    4625:       PetscCall(PetscMalloc2(Nf, &exactSol, Nf, &exactCtx));
    4626:       for (f = 0; f < Nf; ++f) PetscCall(PetscDSGetExactSolution(prob, f, &exactSol[f], &exactCtx[f]));
    4627:       PetscCall(DMComputeL2Diff(dm, 0.0, exactSol, exactCtx, u, &error));
    4628:       PetscCall(PetscFree2(exactSol, exactCtx));
    4629:       if (error < 1.0e-11) PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: < 1.0e-11\n"));
    4630:       else PetscCall(PetscViewerASCIIPrintf(viewer, "L_2 Error: %g\n", (double)error));
    4631:     }
    4632:     if (snes->reason > 0 && format != PETSC_VIEWER_FAILED) {
    4633:       if (((PetscObject)snes)->prefix) {
    4634:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve converged due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4635:       } else {
    4636:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve converged due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4637:       }
    4638:     } else if (snes->reason <= 0) {
    4639:       if (((PetscObject)snes)->prefix) {
    4640:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear %s solve did not converge due to %s iterations %" PetscInt_FMT "\n", ((PetscObject)snes)->prefix, SNESConvergedReasons[snes->reason], snes->iter));
    4641:       } else {
    4642:         PetscCall(PetscViewerASCIIPrintf(viewer, "Nonlinear solve did not converge due to %s iterations %" PetscInt_FMT "\n", SNESConvergedReasons[snes->reason], snes->iter));
    4643:       }
    4644:     }
    4645:     PetscCall(PetscViewerASCIISubtractTab(viewer, ((PetscObject)snes)->tablevel + 1));
    4646:   }
    4647:   PetscFunctionReturn(PETSC_SUCCESS);
    4648: }

    4650: /*@C
    4651:   SNESConvergedReasonViewSet - Sets an ADDITIONAL function that is to be used at the
    4652:   end of the nonlinear solver to display the convergence reason of the nonlinear solver.

    4654:   Logically Collective

    4656:   Input Parameters:
    4657: + snes              - the `SNES` context
    4658: . f                 - the `SNESConvergedReason` view function
    4659: . vctx              - [optional] user-defined context for private data for the `SNESConvergedReason` view function (use `NULL` if no context is desired)
    4660: - reasonviewdestroy - [optional] routine that frees the context (may be `NULL`), see `PetscCtxDestroyFn` for the calling sequence

    4662:   Calling sequence of `f`:
    4663: + snes - the `SNES` context
    4664: - vctx - [optional] context for private data for the function

    4666:   Options Database Keys:
    4667: + -snes_converged_reason             - sets a default `SNESConvergedReasonView()`
    4668: - -snes_converged_reason_view_cancel - cancels all converged reason viewers that have been hardwired into a code by
    4669:                                        calls to `SNESConvergedReasonViewSet()`, but does not cancel those set via the options database.

    4671:   Level: intermediate

    4673:   Note:
    4674:   Several different converged reason view routines may be set by calling
    4675:   `SNESConvergedReasonViewSet()` multiple times; all will be called in the
    4676:   order in which they were set.

    4678: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESConvergedReason`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`, `SNESConvergedReasonViewCancel()`,
    4679:           `PetscCtxDestroyFn`
    4680: @*/
    4681: PetscErrorCode SNESConvergedReasonViewSet(SNES snes, PetscErrorCode (*f)(SNES snes, PetscCtx vctx), PetscCtx vctx, PetscCtxDestroyFn *reasonviewdestroy)
    4682: {
    4683:   PetscFunctionBegin;
    4685:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) {
    4686:     PetscBool identical;

    4688:     PetscCall(PetscMonitorCompare((PetscErrorCode (*)(void))(PetscVoidFn *)f, vctx, reasonviewdestroy, (PetscErrorCode (*)(void))(PetscVoidFn *)snes->reasonview[i], snes->reasonviewcontext[i], snes->reasonviewdestroy[i], &identical));
    4689:     if (identical) PetscFunctionReturn(PETSC_SUCCESS);
    4690:   }
    4691:   PetscCheck(snes->numberreasonviews < MAXSNESREASONVIEWS, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Too many SNES reasonview set");
    4692:   snes->reasonview[snes->numberreasonviews]          = f;
    4693:   snes->reasonviewdestroy[snes->numberreasonviews]   = reasonviewdestroy;
    4694:   snes->reasonviewcontext[snes->numberreasonviews++] = vctx;
    4695:   PetscFunctionReturn(PETSC_SUCCESS);
    4696: }

    4698: /*@
    4699:   SNESConvergedReasonViewFromOptions - Processes command line options to determine if/how a `SNESConvergedReason` is to be viewed at the end of `SNESSolve()`
    4700:   All the user-provided viewer routines set with `SNESConvergedReasonViewSet()` will be called, if they exist.

    4702:   Collective

    4704:   Input Parameter:
    4705: . snes - the `SNES` object

    4707:   Level: advanced

    4709: .seealso: [](ch_snes), `SNES`, `SNESConvergedReason`, `SNESConvergedReasonViewSet()`, `SNESCreate()`, `SNESSetUp()`, `SNESDestroy()`,
    4710:           `SNESSetTolerances()`, `SNESConvergedDefault()`, `SNESGetConvergedReason()`, `SNESConvergedReasonView()`
    4711: @*/
    4712: PetscErrorCode SNESConvergedReasonViewFromOptions(SNES snes)
    4713: {
    4714:   static PetscBool incall = PETSC_FALSE;

    4716:   PetscFunctionBegin;
    4717:   if (incall) PetscFunctionReturn(PETSC_SUCCESS);
    4718:   incall = PETSC_TRUE;

    4720:   /* All user-provided viewers are called first, if they exist. */
    4721:   for (PetscInt i = 0; i < snes->numberreasonviews; i++) PetscCall((*snes->reasonview[i])(snes, snes->reasonviewcontext[i]));

    4723:   /* Call PETSc default routine if users ask for it */
    4724:   if (snes->convergedreasonviewer) {
    4725:     PetscCall(PetscViewerPushFormat(snes->convergedreasonviewer, snes->convergedreasonformat));
    4726:     PetscCall(SNESConvergedReasonView(snes, snes->convergedreasonviewer));
    4727:     PetscCall(PetscViewerPopFormat(snes->convergedreasonviewer));
    4728:   }
    4729:   incall = PETSC_FALSE;
    4730:   PetscFunctionReturn(PETSC_SUCCESS);
    4731: }

    4733: /*@
    4734:   SNESSolve - Solves a nonlinear system $F(x) = b $ associated with a `SNES` object

    4736:   Collective

    4738:   Input Parameters:
    4739: + snes - the `SNES` context
    4740: . b    - the constant part of the equation $F(x) = b$, or `NULL` to use zero.
    4741: - x    - the solution vector.

    4743:   Level: beginner

    4745:   Note:
    4746:   The user should initialize the vector, `x`, with the initial guess
    4747:   for the nonlinear solve prior to calling `SNESSolve()` .

    4749: .seealso: [](ch_snes), `SNES`, `SNESCreate()`, `SNESDestroy()`, `SNESSetFunction()`, `SNESSetJacobian()`, `SNESSetGridSequence()`, `SNESGetSolution()`,
    4750:           `SNESNewtonTRSetPreCheck()`, `SNESNewtonTRGetPreCheck()`, `SNESNewtonTRSetPostCheck()`, `SNESNewtonTRGetPostCheck()`,
    4751:           `SNESLineSearchSetPostCheck()`, `SNESLineSearchGetPostCheck()`, `SNESLineSearchSetPreCheck()`, `SNESLineSearchGetPreCheck()`
    4752: @*/
    4753: PetscErrorCode SNESSolve(SNES snes, Vec b, Vec x)
    4754: {
    4755:   PetscBool flg;
    4756:   PetscInt  grid;
    4757:   Vec       xcreated = NULL;
    4758:   DM        dm;

    4760:   PetscFunctionBegin;
    4763:   if (x) PetscCheckSameComm(snes, 1, x, 3);
    4765:   if (b) PetscCheckSameComm(snes, 1, b, 2);

    4767:   /* High level operations using the nonlinear solver */
    4768:   {
    4769:     PetscViewer       viewer;
    4770:     PetscViewerFormat format;
    4771:     PetscInt          num;
    4772:     PetscBool         flg;
    4773:     static PetscBool  incall = PETSC_FALSE;

    4775:     if (!incall) {
    4776:       /* Estimate the convergence rate of the discretization */
    4777:       PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_convergence_estimate", &viewer, &format, &flg));
    4778:       if (flg) {
    4779:         PetscConvEst conv;
    4780:         DM           dm;
    4781:         PetscReal   *alpha; /* Convergence rate of the solution error for each field in the L_2 norm */
    4782:         PetscInt     Nf;

    4784:         incall = PETSC_TRUE;
    4785:         PetscCall(SNESGetDM(snes, &dm));
    4786:         PetscCall(DMGetNumFields(dm, &Nf));
    4787:         PetscCall(PetscCalloc1(Nf, &alpha));
    4788:         PetscCall(PetscConvEstCreate(PetscObjectComm((PetscObject)snes), &conv));
    4789:         PetscCall(PetscConvEstSetSolver(conv, (PetscObject)snes));
    4790:         PetscCall(PetscConvEstSetFromOptions(conv));
    4791:         PetscCall(PetscConvEstSetUp(conv));
    4792:         PetscCall(PetscConvEstGetConvRate(conv, alpha));
    4793:         PetscCall(PetscViewerPushFormat(viewer, format));
    4794:         PetscCall(PetscConvEstRateView(conv, alpha, viewer));
    4795:         PetscCall(PetscViewerPopFormat(viewer));
    4796:         PetscCall(PetscViewerDestroy(&viewer));
    4797:         PetscCall(PetscConvEstDestroy(&conv));
    4798:         PetscCall(PetscFree(alpha));
    4799:         incall = PETSC_FALSE;
    4800:       }
    4801:       /* Adaptively refine the initial grid */
    4802:       num = 1;
    4803:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_initial", &num, &flg));
    4804:       if (flg) {
    4805:         DMAdaptor adaptor;

    4807:         incall = PETSC_TRUE;
    4808:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4809:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4810:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4811:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4812:         PetscCall(DMAdaptorSetUp(adaptor));
    4813:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_INITIAL, &dm, &x));
    4814:         PetscCall(DMAdaptorDestroy(&adaptor));
    4815:         incall = PETSC_FALSE;
    4816:       }
    4817:       /* Use grid sequencing to adapt */
    4818:       num = 0;
    4819:       PetscCall(PetscOptionsGetInt(NULL, ((PetscObject)snes)->prefix, "-snes_adapt_sequence", &num, NULL));
    4820:       if (num) {
    4821:         DMAdaptor   adaptor;
    4822:         const char *prefix;

    4824:         incall = PETSC_TRUE;
    4825:         PetscCall(DMAdaptorCreate(PetscObjectComm((PetscObject)snes), &adaptor));
    4826:         PetscCall(SNESGetOptionsPrefix(snes, &prefix));
    4827:         PetscCall(DMAdaptorSetOptionsPrefix(adaptor, prefix));
    4828:         PetscCall(DMAdaptorSetSolver(adaptor, snes));
    4829:         PetscCall(DMAdaptorSetSequenceLength(adaptor, num));
    4830:         PetscCall(DMAdaptorSetFromOptions(adaptor));
    4831:         PetscCall(DMAdaptorSetUp(adaptor));
    4832:         PetscCall(PetscObjectViewFromOptions((PetscObject)adaptor, NULL, "-snes_adapt_view"));
    4833:         PetscCall(DMAdaptorAdapt(adaptor, x, DM_ADAPTATION_SEQUENTIAL, &dm, &x));
    4834:         PetscCall(DMAdaptorDestroy(&adaptor));
    4835:         incall = PETSC_FALSE;
    4836:       }
    4837:     }
    4838:   }
    4839:   if (!x) x = snes->vec_sol;
    4840:   if (!x) {
    4841:     PetscCall(SNESGetDM(snes, &dm));
    4842:     PetscCall(DMCreateGlobalVector(dm, &xcreated));
    4843:     x = xcreated;
    4844:   }
    4845:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view_pre"));

    4847:   for (grid = 0; grid < snes->gridsequence; grid++) PetscCall(PetscViewerASCIIPushTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4848:   for (grid = 0; grid < snes->gridsequence + 1; grid++) {
    4849:     /* set solution vector */
    4850:     if (!grid) PetscCall(PetscObjectReference((PetscObject)x));
    4851:     PetscCall(VecDestroy(&snes->vec_sol));
    4852:     snes->vec_sol = x;
    4853:     PetscCall(SNESGetDM(snes, &dm));

    4855:     /* set affine vector if provided */
    4856:     PetscCall(PetscObjectReference((PetscObject)b));
    4857:     PetscCall(VecDestroy(&snes->vec_rhs));
    4858:     snes->vec_rhs = b;

    4860:     if (snes->vec_rhs) PetscCheck(snes->vec_func != snes->vec_rhs, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Right hand side vector cannot be function vector");
    4861:     PetscCheck(snes->vec_func != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be function vector");
    4862:     PetscCheck(snes->vec_rhs != snes->vec_sol, PETSC_COMM_SELF, PETSC_ERR_ARG_IDN, "Solution vector cannot be right-hand side vector");
    4863:     if (!snes->vec_sol_update /* && snes->vec_sol */) PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_sol_update));
    4864:     PetscCall(DMShellSetGlobalVector(dm, snes->vec_sol));
    4865:     PetscCall(SNESSetUp(snes));

    4867:     if (!grid) {
    4868:       if (snes->ops->computeinitialguess) PetscCallBack("SNES callback compute initial guess", (*snes->ops->computeinitialguess)(snes, snes->vec_sol, snes->initialguessP));
    4869:     }

    4871:     if (snes->conv_hist_reset) snes->conv_hist_len = 0;
    4872:     PetscCall(SNESResetCounters(snes));
    4873:     snes->reason = SNES_CONVERGED_ITERATING;
    4874:     PetscCall(PetscLogEventBegin(SNES_Solve, snes, 0, 0, 0));
    4875:     PetscUseTypeMethod(snes, solve);
    4876:     PetscCall(PetscLogEventEnd(SNES_Solve, snes, 0, 0, 0));
    4877:     PetscCheck(snes->reason, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Internal error, solver %s returned without setting converged reason", ((PetscObject)snes)->type_name);
    4878:     snes->functiondomainerror  = PETSC_FALSE; /* clear the flag if it has been set */
    4879:     snes->objectivedomainerror = PETSC_FALSE; /* clear the flag if it has been set */
    4880:     snes->jacobiandomainerror  = PETSC_FALSE; /* clear the flag if it has been set */

    4882:     if (snes->lagjac_persist) snes->jac_iter += snes->iter;
    4883:     if (snes->lagpre_persist) snes->pre_iter += snes->iter;

    4885:     PetscCall(PetscOptionsCreateViewer(PetscObjectComm((PetscObject)snes), ((PetscObject)snes)->options, ((PetscObject)snes)->prefix, "-snes_test_local_min", NULL, NULL, &flg));
    4886:     if (flg && !PetscPreLoadingOn) PetscCall(SNESTestLocalMin(snes));
    4887:     /* Call converged reason views. This may involve user-provided viewers as well */
    4888:     PetscCall(SNESConvergedReasonViewFromOptions(snes));

    4890:     if (snes->errorifnotconverged) {
    4891:       if (snes->reason < 0) PetscCall(SNESMonitorCancel(snes));
    4892:       PetscCheck(snes->reason >= 0, PetscObjectComm((PetscObject)snes), PETSC_ERR_NOT_CONVERGED, "SNESSolve has not converged");
    4893:     }
    4894:     if (snes->reason < 0) break;
    4895:     if (grid < snes->gridsequence) {
    4896:       DM  fine;
    4897:       Vec xnew;
    4898:       Mat interp;

    4900:       PetscCall(DMRefine(snes->dm, PetscObjectComm((PetscObject)snes), &fine));
    4901:       PetscCheck(fine, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_INCOMP, "DMRefine() did not perform any refinement, cannot continue grid sequencing");
    4902:       PetscCall(DMGetCoordinatesLocalSetUp(fine));
    4903:       PetscCall(DMCreateInterpolation(snes->dm, fine, &interp, NULL));
    4904:       PetscCall(DMCreateGlobalVector(fine, &xnew));
    4905:       PetscCall(MatInterpolate(interp, x, xnew));
    4906:       PetscCall(DMInterpolate(snes->dm, interp, fine));
    4907:       PetscCall(MatDestroy(&interp));
    4908:       x = xnew;

    4910:       PetscCall(SNESReset(snes));
    4911:       PetscCall(SNESSetDM(snes, fine));
    4912:       PetscCall(SNESResetFromOptions(snes));
    4913:       PetscCall(DMDestroy(&fine));
    4914:       PetscCall(PetscViewerASCIIPopTab(PETSC_VIEWER_STDOUT_(PetscObjectComm((PetscObject)snes))));
    4915:     }
    4916:   }
    4917:   PetscCall(SNESViewFromOptions(snes, NULL, "-snes_view"));
    4918:   PetscCall(VecViewFromOptions(snes->vec_sol, (PetscObject)snes, "-snes_view_solution"));
    4919:   PetscCall(DMMonitor(snes->dm));
    4920:   PetscCall(SNESMonitorPauseFinal_Internal(snes));

    4922:   PetscCall(VecDestroy(&xcreated));
    4923:   PetscCall(PetscObjectSAWsBlock((PetscObject)snes));
    4924:   PetscFunctionReturn(PETSC_SUCCESS);
    4925: }

    4927: /* --------- Internal routines for SNES Package --------- */

    4929: /*@
    4930:   SNESSetType - Sets the algorithm/method to be used to solve the nonlinear system with the given `SNES`

    4932:   Collective

    4934:   Input Parameters:
    4935: + snes - the `SNES` context
    4936: - type - a known method

    4938:   Options Database Key:
    4939: . -snes_type type - Sets the method; see `SNESType`

    4941:   Level: intermediate

    4943:   Notes:
    4944:   See `SNESType` for available methods (for instance)
    4945: +    `SNESNEWTONLS` - Newton's method with line search
    4946:   (systems of nonlinear equations)
    4947: -    `SNESNEWTONTR` - Newton's method with trust region
    4948:   (systems of nonlinear equations)

    4950:   Normally, it is best to use the `SNESSetFromOptions()` command and then
    4951:   set the `SNES` solver type from the options database rather than by using
    4952:   this routine.  Using the options database provides the user with
    4953:   maximum flexibility in evaluating the many nonlinear solvers.
    4954:   The `SNESSetType()` routine is provided for those situations where it
    4955:   is necessary to set the nonlinear solver independently of the command
    4956:   line or options database.  This might be the case, for example, when
    4957:   the choice of solver changes during the execution of the program,
    4958:   and the user's application is taking responsibility for choosing the
    4959:   appropriate method.

    4961:   Developer Note:
    4962:   `SNESRegister()` adds a constructor for a new `SNESType` to `SNESList`, `SNESSetType()` locates
    4963:   the constructor in that list and calls it to create the specific object.

    4965: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESType`, `SNESCreate()`, `SNESDestroy()`, `SNESGetType()`, `SNESSetFromOptions()`
    4966: @*/
    4967: PetscErrorCode SNESSetType(SNES snes, SNESType type)
    4968: {
    4969:   PetscBool match;
    4970:   PetscErrorCode (*r)(SNES);

    4972:   PetscFunctionBegin;
    4974:   PetscAssertPointer(type, 2);

    4976:   PetscCall(PetscObjectTypeCompare((PetscObject)snes, type, &match));
    4977:   if (match) PetscFunctionReturn(PETSC_SUCCESS);

    4979:   PetscCall(PetscFunctionListFind(SNESList, type, &r));
    4980:   PetscCheck(r, PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_UNKNOWN_TYPE, "Unable to find requested SNES type %s", type);
    4981:   /* Destroy the previous private SNES context */
    4982:   PetscTryTypeMethod(snes, destroy);
    4983:   /* Reinitialize type-specific function pointers in SNESOps structure */
    4984:   snes->ops->reset          = NULL;
    4985:   snes->ops->setup          = NULL;
    4986:   snes->ops->solve          = NULL;
    4987:   snes->ops->view           = NULL;
    4988:   snes->ops->setfromoptions = NULL;
    4989:   snes->ops->destroy        = NULL;

    4991:   /* It may happen the user has customized the line search before calling SNESSetType */
    4992:   if (((PetscObject)snes)->type_name) PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    4994:   /* Call the SNESCreate_XXX routine for this particular Nonlinear solver */
    4995:   snes->setupcalled = PETSC_FALSE;

    4997:   PetscCall(PetscObjectChangeTypeName((PetscObject)snes, type));
    4998:   PetscCall((*r)(snes));
    4999:   PetscFunctionReturn(PETSC_SUCCESS);
    5000: }

    5002: /*@
    5003:   SNESGetType - Gets the `SNES` method type and name (as a string).

    5005:   Not Collective

    5007:   Input Parameter:
    5008: . snes - nonlinear solver context

    5010:   Output Parameter:
    5011: . type - `SNES` method (a character string)

    5013:   Level: intermediate

    5015: .seealso: [](ch_snes), `SNESSetType()`, `SNESType`, `SNESSetFromOptions()`, `SNES`
    5016: @*/
    5017: PetscErrorCode SNESGetType(SNES snes, SNESType *type)
    5018: {
    5019:   PetscFunctionBegin;
    5021:   PetscAssertPointer(type, 2);
    5022:   *type = ((PetscObject)snes)->type_name;
    5023:   PetscFunctionReturn(PETSC_SUCCESS);
    5024: }

    5026: /*@
    5027:   SNESSetSolution - Sets the solution vector for use by the `SNES` routines.

    5029:   Logically Collective

    5031:   Input Parameters:
    5032: + snes - the `SNES` context obtained from `SNESCreate()`
    5033: - u    - the solution vector

    5035:   Level: beginner

    5037: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESGetSolution()`, `Vec`
    5038: @*/
    5039: PetscErrorCode SNESSetSolution(SNES snes, Vec u)
    5040: {
    5041:   DM dm;

    5043:   PetscFunctionBegin;
    5046:   PetscCall(PetscObjectReference((PetscObject)u));
    5047:   PetscCall(VecDestroy(&snes->vec_sol));

    5049:   snes->vec_sol = u;

    5051:   PetscCall(SNESGetDM(snes, &dm));
    5052:   PetscCall(DMShellSetGlobalVector(dm, u));
    5053:   PetscFunctionReturn(PETSC_SUCCESS);
    5054: }

    5056: /*@
    5057:   SNESGetSolution - Returns the vector where the approximate solution is
    5058:   stored. This is the fine grid solution when using `SNESSetGridSequence()`.

    5060:   Not Collective, but `x` is parallel if `snes` is parallel

    5062:   Input Parameter:
    5063: . snes - the `SNES` context

    5065:   Output Parameter:
    5066: . x - the solution

    5068:   Level: intermediate

    5070: .seealso: [](ch_snes), `SNESSetSolution()`, `SNESSolve()`, `SNES`, `SNESGetSolutionUpdate()`, `SNESGetFunction()`
    5071: @*/
    5072: PetscErrorCode SNESGetSolution(SNES snes, Vec *x)
    5073: {
    5074:   PetscFunctionBegin;
    5076:   PetscAssertPointer(x, 2);
    5077:   *x = snes->vec_sol;
    5078:   PetscFunctionReturn(PETSC_SUCCESS);
    5079: }

    5081: /*@
    5082:   SNESGetSolutionUpdate - Returns the vector where the solution update is
    5083:   stored.

    5085:   Not Collective, but `x` is parallel if `snes` is parallel

    5087:   Input Parameter:
    5088: . snes - the `SNES` context

    5090:   Output Parameter:
    5091: . x - the solution update

    5093:   Level: advanced

    5095: .seealso: [](ch_snes), `SNES`, `SNESGetSolution()`, `SNESGetFunction()`
    5096: @*/
    5097: PetscErrorCode SNESGetSolutionUpdate(SNES snes, Vec *x)
    5098: {
    5099:   PetscFunctionBegin;
    5101:   PetscAssertPointer(x, 2);
    5102:   *x = snes->vec_sol_update;
    5103:   PetscFunctionReturn(PETSC_SUCCESS);
    5104: }

    5106: /*@C
    5107:   SNESGetFunction - Returns the function that defines the nonlinear system set with `SNESSetFunction()`

    5109:   Not Collective, but `r` is parallel if `snes` is parallel. Collective if `r` is requested, but has not been created yet.

    5111:   Input Parameter:
    5112: . snes - the `SNES` context

    5114:   Output Parameters:
    5115: + r   - the vector that is used to store residuals (or `NULL` if you don't want it)
    5116: . f   - the function (or `NULL` if you don't want it);  for calling sequence see `SNESFunctionFn`
    5117: - ctx - the function context (or `NULL` if you don't want it)

    5119:   Level: advanced

    5121:   Note:
    5122:   The vector `r` DOES NOT, in general, contain the current value of the `SNES` nonlinear function

    5124: .seealso: [](ch_snes), `SNES`, `SNESSolve()`, `SNESSetFunction()`, `SNESGetSolution()`, `SNESFunctionFn`
    5125: @*/
    5126: PetscErrorCode SNESGetFunction(SNES snes, Vec *r, SNESFunctionFn **f, PetscCtxRt ctx)
    5127: {
    5128:   DM dm;

    5130:   PetscFunctionBegin;
    5132:   if (r) {
    5133:     if (!snes->vec_func) {
    5134:       if (snes->vec_rhs) {
    5135:         PetscCall(VecDuplicate(snes->vec_rhs, &snes->vec_func));
    5136:       } else if (snes->vec_sol) {
    5137:         PetscCall(VecDuplicate(snes->vec_sol, &snes->vec_func));
    5138:       } else if (snes->dm) {
    5139:         PetscCall(DMCreateGlobalVector(snes->dm, &snes->vec_func));
    5140:       }
    5141:     }
    5142:     *r = snes->vec_func;
    5143:   }
    5144:   PetscCall(SNESGetDM(snes, &dm));
    5145:   PetscCall(DMSNESGetFunction(dm, f, ctx));
    5146:   PetscFunctionReturn(PETSC_SUCCESS);
    5147: }

    5149: /*@C
    5150:   SNESGetNGS - Returns the function and context set with `SNESSetNGS()`

    5152:   Input Parameter:
    5153: . snes - the `SNES` context

    5155:   Output Parameters:
    5156: + f   - the function (or `NULL`) see `SNESNGSFn` for calling sequence
    5157: - ctx - the function context (or `NULL`)

    5159:   Level: advanced

    5161: .seealso: [](ch_snes), `SNESSetNGS()`, `SNESGetFunction()`, `SNESNGSFn`
    5162: @*/
    5163: PetscErrorCode SNESGetNGS(SNES snes, SNESNGSFn **f, PetscCtxRt ctx)
    5164: {
    5165:   DM dm;

    5167:   PetscFunctionBegin;
    5169:   PetscCall(SNESGetDM(snes, &dm));
    5170:   PetscCall(DMSNESGetNGS(dm, f, ctx));
    5171:   PetscFunctionReturn(PETSC_SUCCESS);
    5172: }

    5174: /*@
    5175:   SNESSetOptionsPrefix - Sets the prefix used for searching for all
    5176:   `SNES` options in the database.

    5178:   Logically Collective

    5180:   Input Parameters:
    5181: + snes   - the `SNES` context
    5182: - prefix - the prefix to prepend to all option names

    5184:   Level: advanced

    5186:   Note:
    5187:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5188:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5190: .seealso: [](ch_snes), `SNES`, `SNESSetFromOptions()`, `SNESAppendOptionsPrefix()`
    5191: @*/
    5192: PetscErrorCode SNESSetOptionsPrefix(SNES snes, const char prefix[])
    5193: {
    5194:   PetscFunctionBegin;
    5196:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes, prefix));
    5197:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5198:   if (snes->linesearch) {
    5199:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5200:     PetscCall(PetscObjectSetOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5201:   }
    5202:   PetscCall(KSPSetOptionsPrefix(snes->ksp, prefix));
    5203:   PetscFunctionReturn(PETSC_SUCCESS);
    5204: }

    5206: /*@
    5207:   SNESAppendOptionsPrefix - Appends to the prefix used for searching for all
    5208:   `SNES` options in the database.

    5210:   Logically Collective

    5212:   Input Parameters:
    5213: + snes   - the `SNES` context
    5214: - prefix - the prefix to prepend to all option names

    5216:   Level: advanced

    5218:   Note:
    5219:   A hyphen (-) must NOT be given at the beginning of the prefix name.
    5220:   The first character of all runtime options is AUTOMATICALLY the hyphen.

    5222: .seealso: [](ch_snes), `SNESGetOptionsPrefix()`, `SNESSetOptionsPrefix()`
    5223: @*/
    5224: PetscErrorCode SNESAppendOptionsPrefix(SNES snes, const char prefix[])
    5225: {
    5226:   PetscFunctionBegin;
    5228:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes, prefix));
    5229:   if (!snes->ksp) PetscCall(SNESGetKSP(snes, &snes->ksp));
    5230:   if (snes->linesearch) {
    5231:     PetscCall(SNESGetLineSearch(snes, &snes->linesearch));
    5232:     PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)snes->linesearch, prefix));
    5233:   }
    5234:   PetscCall(KSPAppendOptionsPrefix(snes->ksp, prefix));
    5235:   PetscFunctionReturn(PETSC_SUCCESS);
    5236: }

    5238: /*@
    5239:   SNESGetOptionsPrefix - Gets the prefix used for searching for all
    5240:   `SNES` options in the database.

    5242:   Not Collective

    5244:   Input Parameter:
    5245: . snes - the `SNES` context

    5247:   Output Parameter:
    5248: . prefix - pointer to the prefix string used

    5250:   Level: advanced

    5252: .seealso: [](ch_snes), `SNES`, `SNESSetOptionsPrefix()`, `SNESAppendOptionsPrefix()`
    5253: @*/
    5254: PetscErrorCode SNESGetOptionsPrefix(SNES snes, const char *prefix[])
    5255: {
    5256:   PetscFunctionBegin;
    5258:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)snes, prefix));
    5259:   PetscFunctionReturn(PETSC_SUCCESS);
    5260: }

    5262: /*@C
    5263:   SNESRegister - Adds a method to the nonlinear solver package.

    5265:   Not Collective

    5267:   Input Parameters:
    5268: + sname    - name of a new user-defined solver
    5269: - function - routine to create method context

    5271:   Level: advanced

    5273:   Note:
    5274:   `SNESRegister()` may be called multiple times to add several user-defined solvers.

    5276:   Example Usage:
    5277: .vb
    5278:    SNESRegister("my_solver", MySolverCreate);
    5279: .ve

    5281:   Then, your solver can be chosen with the procedural interface via
    5282: .vb
    5283:   SNESSetType(snes, "my_solver")
    5284: .ve
    5285:   or at runtime via the option
    5286: .vb
    5287:   -snes_type my_solver
    5288: .ve

    5290: .seealso: [](ch_snes), `SNESRegisterAll()`, `SNESRegisterDestroy()`
    5291: @*/
    5292: PetscErrorCode SNESRegister(const char sname[], PetscErrorCode (*function)(SNES))
    5293: {
    5294:   PetscFunctionBegin;
    5295:   PetscCall(SNESInitializePackage());
    5296:   PetscCall(PetscFunctionListAdd(&SNESList, sname, function));
    5297:   PetscFunctionReturn(PETSC_SUCCESS);
    5298: }

    5300: PetscErrorCode SNESTestLocalMin(SNES snes)
    5301: {
    5302:   PetscInt    N, i, j;
    5303:   Vec         u, uh, fh;
    5304:   PetscScalar value;
    5305:   PetscReal   norm;

    5307:   PetscFunctionBegin;
    5308:   PetscCall(SNESGetSolution(snes, &u));
    5309:   PetscCall(VecDuplicate(u, &uh));
    5310:   PetscCall(VecDuplicate(u, &fh));

    5312:   /* currently only works for sequential */
    5313:   PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "Testing FormFunction() for local min\n"));
    5314:   PetscCall(VecGetSize(u, &N));
    5315:   for (i = 0; i < N; i++) {
    5316:     PetscCall(VecCopy(u, uh));
    5317:     PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "i = %" PetscInt_FMT "\n", i));
    5318:     for (j = -10; j < 11; j++) {
    5319:       value = PetscSign(j) * PetscExpReal(PetscAbs(j) - 10.0);
    5320:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5321:       PetscCall(SNESComputeFunction(snes, uh, fh));
    5322:       PetscCall(VecNorm(fh, NORM_2, &norm)); /* does not handle use of SNESSetFunctionDomainError() correctly */
    5323:       PetscCall(PetscPrintf(PetscObjectComm((PetscObject)snes), "       j norm %" PetscInt_FMT " %18.16e\n", j, (double)norm));
    5324:       value = -value;
    5325:       PetscCall(VecSetValue(uh, i, value, ADD_VALUES));
    5326:     }
    5327:   }
    5328:   PetscCall(VecDestroy(&uh));
    5329:   PetscCall(VecDestroy(&fh));
    5330:   PetscFunctionReturn(PETSC_SUCCESS);
    5331: }

    5333: /*@
    5334:   SNESGetLineSearch - Returns the line search associated with the `SNES`.

    5336:   Not Collective

    5338:   Input Parameter:
    5339: . snes - iterative context obtained from `SNESCreate()`

    5341:   Output Parameter:
    5342: . linesearch - linesearch context

    5344:   Level: beginner

    5346:   Notes:
    5347:   It creates a default line search instance which can be configured as needed in case it has not been already set with `SNESSetLineSearch()`.

    5349:   You can also use the options database keys `-snes_linesearch_*` to configure the line search. See `SNESLineSearchSetFromOptions()` for the possible options.

    5351: .seealso: [](ch_snes), `SNESLineSearch`, `SNESSetLineSearch()`, `SNESLineSearchCreate()`, `SNESLineSearchSetFromOptions()`
    5352: @*/
    5353: PetscErrorCode SNESGetLineSearch(SNES snes, SNESLineSearch *linesearch)
    5354: {
    5355:   const char *optionsprefix;

    5357:   PetscFunctionBegin;
    5359:   PetscAssertPointer(linesearch, 2);
    5360:   if (!snes->linesearch) {
    5361:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5362:     PetscCall(SNESLineSearchCreate(PetscObjectComm((PetscObject)snes), &snes->linesearch));
    5363:     PetscCall(SNESLineSearchSetSNES(snes->linesearch, snes));
    5364:     PetscCall(SNESLineSearchAppendOptionsPrefix(snes->linesearch, optionsprefix));
    5365:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->linesearch, (PetscObject)snes, 1));
    5366:   }
    5367:   *linesearch = snes->linesearch;
    5368:   PetscFunctionReturn(PETSC_SUCCESS);
    5369: }

    5371: /*@
    5372:   SNESKSPSetUseEW - Sets `SNES` to the use Eisenstat-Walker method for
    5373:   computing relative tolerance for linear solvers within an inexact
    5374:   Newton method.

    5376:   Logically Collective

    5378:   Input Parameters:
    5379: + snes - `SNES` context
    5380: - flag - `PETSC_TRUE` or `PETSC_FALSE`

    5382:   Options Database Keys:
    5383: + -snes_ksp_ew                     - use Eisenstat-Walker method for determining linear system convergence
    5384: . -snes_ksp_ew_version ver         - version of  Eisenstat-Walker method
    5385: . -snes_ksp_ew_rtol0 rtol0         - Sets rtol0
    5386: . -snes_ksp_ew_rtolmax rtolmax     - Sets rtolmax
    5387: . -snes_ksp_ew_gamma gamma         - Sets gamma
    5388: . -snes_ksp_ew_alpha alpha         - Sets alpha
    5389: . -snes_ksp_ew_alpha2 alpha2       - Sets alpha2
    5390: - -snes_ksp_ew_threshold threshold - Sets threshold

    5392:   Level: advanced

    5394:   Note:
    5395:   The default is to use a constant relative tolerance for
    5396:   the inner linear solvers.  Alternatively, one can use the
    5397:   Eisenstat-Walker method {cite}`ew96`, where the relative convergence tolerance
    5398:   is reset at each Newton iteration according progress of the nonlinear
    5399:   solver.

    5401: .seealso: [](ch_snes), `KSP`, `SNES`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5402: @*/
    5403: PetscErrorCode SNESKSPSetUseEW(SNES snes, PetscBool flag)
    5404: {
    5405:   PetscFunctionBegin;
    5408:   snes->ksp_ewconv = flag;
    5409:   PetscFunctionReturn(PETSC_SUCCESS);
    5410: }

    5412: /*@
    5413:   SNESKSPGetUseEW - Gets if `SNES` is using Eisenstat-Walker method
    5414:   for computing relative tolerance for linear solvers within an
    5415:   inexact Newton method.

    5417:   Not Collective

    5419:   Input Parameter:
    5420: . snes - `SNES` context

    5422:   Output Parameter:
    5423: . flag - `PETSC_TRUE` or `PETSC_FALSE`

    5425:   Level: advanced

    5427: .seealso: [](ch_snes), `SNESKSPSetUseEW()`, `SNESKSPGetParametersEW()`, `SNESKSPSetParametersEW()`
    5428: @*/
    5429: PetscErrorCode SNESKSPGetUseEW(SNES snes, PetscBool *flag)
    5430: {
    5431:   PetscFunctionBegin;
    5433:   PetscAssertPointer(flag, 2);
    5434:   *flag = snes->ksp_ewconv;
    5435:   PetscFunctionReturn(PETSC_SUCCESS);
    5436: }

    5438: /*@
    5439:   SNESKSPSetParametersEW - Sets parameters for Eisenstat-Walker
    5440:   convergence criteria for the linear solvers within an inexact
    5441:   Newton method.

    5443:   Logically Collective

    5445:   Input Parameters:
    5446: + snes      - `SNES` context
    5447: . version   - version 1, 2 (default is 2), 3 or 4
    5448: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5449: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5450: . gamma     - multiplicative factor for version 2 rtol computation
    5451:              (0 <= gamma2 <= 1)
    5452: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5453: . alpha2    - power for safeguard
    5454: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5456:   Level: advanced

    5458:   Notes:
    5459:   Version 3 was contributed by Luis Chacon, June 2006.

    5461:   Use `PETSC_CURRENT` to retain the default for any of the parameters.

    5463: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPGetParametersEW()`
    5464: @*/
    5465: PetscErrorCode SNESKSPSetParametersEW(SNES snes, PetscInt version, PetscReal rtol_0, PetscReal rtol_max, PetscReal gamma, PetscReal alpha, PetscReal alpha2, PetscReal threshold)
    5466: {
    5467:   SNESKSPEW *kctx;

    5469:   PetscFunctionBegin;
    5471:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5472:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");

    5481:   if (version != PETSC_CURRENT) kctx->version = version;
    5482:   if (rtol_0 != (PetscReal)PETSC_CURRENT) kctx->rtol_0 = rtol_0;
    5483:   if (rtol_max != (PetscReal)PETSC_CURRENT) kctx->rtol_max = rtol_max;
    5484:   if (gamma != (PetscReal)PETSC_CURRENT) kctx->gamma = gamma;
    5485:   if (alpha != (PetscReal)PETSC_CURRENT) kctx->alpha = alpha;
    5486:   if (alpha2 != (PetscReal)PETSC_CURRENT) kctx->alpha2 = alpha2;
    5487:   if (threshold != (PetscReal)PETSC_CURRENT) kctx->threshold = threshold;

    5489:   PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1 to 4 are supported: %" PetscInt_FMT, kctx->version);
    5490:   PetscCheck(kctx->rtol_0 >= 0.0 && kctx->rtol_0 < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_0 < 1.0: %g", (double)kctx->rtol_0);
    5491:   PetscCheck(kctx->rtol_max >= 0.0 && kctx->rtol_max < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= rtol_max (%g) < 1.0", (double)kctx->rtol_max);
    5492:   PetscCheck(kctx->gamma >= 0.0 && kctx->gamma <= 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 <= gamma (%g) <= 1.0", (double)kctx->gamma);
    5493:   PetscCheck(kctx->alpha > 1.0 && kctx->alpha <= 2.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "1.0 < alpha (%g) <= 2.0", (double)kctx->alpha);
    5494:   PetscCheck(kctx->threshold > 0.0 && kctx->threshold < 1.0, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "0.0 < threshold (%g) < 1.0", (double)kctx->threshold);
    5495:   PetscFunctionReturn(PETSC_SUCCESS);
    5496: }

    5498: /*@
    5499:   SNESKSPGetParametersEW - Gets parameters for Eisenstat-Walker
    5500:   convergence criteria for the linear solvers within an inexact
    5501:   Newton method.

    5503:   Not Collective

    5505:   Input Parameter:
    5506: . snes - `SNES` context

    5508:   Output Parameters:
    5509: + version   - version 1, 2 (default is 2), 3 or 4
    5510: . rtol_0    - initial relative tolerance (0 <= rtol_0 < 1)
    5511: . rtol_max  - maximum relative tolerance (0 <= rtol_max < 1)
    5512: . gamma     - multiplicative factor for version 2 rtol computation (0 <= gamma2 <= 1)
    5513: . alpha     - power for version 2 rtol computation (1 < alpha <= 2)
    5514: . alpha2    - power for safeguard
    5515: - threshold - threshold for imposing safeguard (0 < threshold < 1)

    5517:   Level: advanced

    5519: .seealso: [](ch_snes), `SNES`, `SNESKSPSetUseEW()`, `SNESKSPGetUseEW()`, `SNESKSPSetParametersEW()`
    5520: @*/
    5521: PetscErrorCode SNESKSPGetParametersEW(SNES snes, PetscInt *version, PetscReal *rtol_0, PetscReal *rtol_max, PetscReal *gamma, PetscReal *alpha, PetscReal *alpha2, PetscReal *threshold)
    5522: {
    5523:   SNESKSPEW *kctx;

    5525:   PetscFunctionBegin;
    5527:   kctx = (SNESKSPEW *)snes->kspconvctx;
    5528:   PetscCheck(kctx, PETSC_COMM_SELF, PETSC_ERR_ARG_WRONGSTATE, "No Eisenstat-Walker context existing");
    5529:   if (version) *version = kctx->version;
    5530:   if (rtol_0) *rtol_0 = kctx->rtol_0;
    5531:   if (rtol_max) *rtol_max = kctx->rtol_max;
    5532:   if (gamma) *gamma = kctx->gamma;
    5533:   if (alpha) *alpha = kctx->alpha;
    5534:   if (alpha2) *alpha2 = kctx->alpha2;
    5535:   if (threshold) *threshold = kctx->threshold;
    5536:   PetscFunctionReturn(PETSC_SUCCESS);
    5537: }

    5539: PetscErrorCode KSPPreSolve_SNESEW(KSP ksp, Vec b, Vec x, PetscCtx ctx)
    5540: {
    5541:   SNES       snes = (SNES)ctx;
    5542:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5543:   PetscReal  rtol = PETSC_CURRENT, stol;

    5545:   PetscFunctionBegin;
    5546:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5547:   if (!snes->iter) {
    5548:     rtol = kctx->rtol_0; /* first time in, so use the original user rtol */
    5549:     PetscCall(VecNorm(snes->vec_func, NORM_2, &kctx->norm_first));
    5550:   } else {
    5551:     PetscCheck(kctx->version >= 1 && kctx->version <= 4, PETSC_COMM_SELF, PETSC_ERR_ARG_OUTOFRANGE, "Only versions 1-4 are supported: %" PetscInt_FMT, kctx->version);
    5552:     if (kctx->version == 1) {
    5553:       rtol = PetscAbsReal(snes->norm - kctx->lresid_last) / kctx->norm_last;
    5554:       stol = PetscPowReal(kctx->rtol_last, kctx->alpha2);
    5555:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5556:     } else if (kctx->version == 2) {
    5557:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5558:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5559:       if (stol > kctx->threshold) rtol = PetscMax(rtol, stol);
    5560:     } else if (kctx->version == 3) { /* contributed by Luis Chacon, June 2006. */
    5561:       rtol = kctx->gamma * PetscPowReal(snes->norm / kctx->norm_last, kctx->alpha);
    5562:       /* safeguard: avoid sharp decrease of rtol */
    5563:       stol = kctx->gamma * PetscPowReal(kctx->rtol_last, kctx->alpha);
    5564:       stol = PetscMax(rtol, stol);
    5565:       rtol = PetscMin(kctx->rtol_0, stol);
    5566:       /* safeguard: avoid oversolving */
    5567:       stol = kctx->gamma * (kctx->norm_first * snes->rtol) / snes->norm;
    5568:       stol = PetscMax(rtol, stol);
    5569:       rtol = PetscMin(kctx->rtol_0, stol);
    5570:     } else /* if (kctx->version == 4) */ {
    5571:       /* H.-B. An et al. Journal of Computational and Applied Mathematics 200 (2007) 47-60 */
    5572:       PetscReal ared = PetscAbsReal(kctx->norm_last - snes->norm);
    5573:       PetscReal pred = PetscAbsReal(kctx->norm_last - kctx->lresid_last);
    5574:       PetscReal rk   = ared / pred;
    5575:       if (rk < kctx->v4_p1) rtol = 1. - 2. * kctx->v4_p1;
    5576:       else if (rk < kctx->v4_p2) rtol = kctx->rtol_last;
    5577:       else if (rk < kctx->v4_p3) rtol = kctx->v4_m1 * kctx->rtol_last;
    5578:       else rtol = kctx->v4_m2 * kctx->rtol_last;

    5580:       if (kctx->rtol_last_2 > kctx->v4_m3 && kctx->rtol_last > kctx->v4_m3 && kctx->rk_last_2 < kctx->v4_p1 && kctx->rk_last < kctx->v4_p1) rtol = kctx->v4_m4 * kctx->rtol_last;
    5581:       kctx->rtol_last_2 = kctx->rtol_last;
    5582:       kctx->rk_last_2   = kctx->rk_last;
    5583:       kctx->rk_last     = rk;
    5584:     }
    5585:   }
    5586:   /* safeguard: avoid rtol greater than rtol_max */
    5587:   rtol = PetscMin(rtol, kctx->rtol_max);
    5588:   PetscCall(KSPSetTolerances(ksp, rtol, PETSC_CURRENT, PETSC_CURRENT, PETSC_CURRENT));
    5589:   PetscCall(PetscInfo(snes, "iter %" PetscInt_FMT ", Eisenstat-Walker (version %" PetscInt_FMT ") KSP rtol=%g\n", snes->iter, kctx->version, (double)rtol));
    5590:   PetscFunctionReturn(PETSC_SUCCESS);
    5591: }

    5593: PetscErrorCode KSPPostSolve_SNESEW(KSP ksp, Vec b, Vec x, PetscCtx ctx)
    5594: {
    5595:   SNES       snes = (SNES)ctx;
    5596:   SNESKSPEW *kctx = (SNESKSPEW *)snes->kspconvctx;
    5597:   PCSide     pcside;
    5598:   Vec        lres;

    5600:   PetscFunctionBegin;
    5601:   if (!snes->ksp_ewconv) PetscFunctionReturn(PETSC_SUCCESS);
    5602:   PetscCall(KSPGetTolerances(ksp, &kctx->rtol_last, NULL, NULL, NULL));
    5603:   kctx->norm_last = snes->norm;
    5604:   if (kctx->version == 1 || kctx->version == 4) {
    5605:     PC        pc;
    5606:     PetscBool getRes;

    5608:     PetscCall(KSPGetPC(ksp, &pc));
    5609:     PetscCall(PetscObjectTypeCompare((PetscObject)pc, PCNONE, &getRes));
    5610:     if (!getRes) {
    5611:       KSPNormType normtype;

    5613:       PetscCall(KSPGetNormType(ksp, &normtype));
    5614:       getRes = (PetscBool)(normtype == KSP_NORM_UNPRECONDITIONED);
    5615:     }
    5616:     PetscCall(KSPGetPCSide(ksp, &pcside));
    5617:     if (pcside == PC_RIGHT || getRes) { /* KSP residual is true linear residual */
    5618:       PetscCall(KSPGetResidualNorm(ksp, &kctx->lresid_last));
    5619:     } else {
    5620:       /* KSP residual is preconditioned residual */
    5621:       /* compute true linear residual norm */
    5622:       Mat J;
    5623:       PetscCall(KSPGetOperators(ksp, &J, NULL));
    5624:       PetscCall(VecDuplicate(b, &lres));
    5625:       PetscCall(MatMult(J, x, lres));
    5626:       PetscCall(VecAYPX(lres, -1.0, b));
    5627:       PetscCall(VecNorm(lres, NORM_2, &kctx->lresid_last));
    5628:       PetscCall(VecDestroy(&lres));
    5629:     }
    5630:   }
    5631:   PetscFunctionReturn(PETSC_SUCCESS);
    5632: }

    5634: /*@
    5635:   SNESGetKSP - Returns the `KSP` context for a `SNES` solver.

    5637:   Not Collective, but if `snes` is parallel, then `ksp` is parallel

    5639:   Input Parameter:
    5640: . snes - the `SNES` context

    5642:   Output Parameter:
    5643: . ksp - the `KSP` context

    5645:   Level: beginner

    5647:   Notes:
    5648:   The user can then directly manipulate the `KSP` context to set various
    5649:   options, etc.  Likewise, the user can then extract and manipulate the
    5650:   `PC` contexts as well.

    5652:   Some `SNESType`s do not use a `KSP` but a `KSP` is still returned by this function, changes to that `KSP` will have no effect.

    5654: .seealso: [](ch_snes), `SNES`, `KSP`, `PC`, `KSPGetPC()`, `SNESCreate()`, `KSPCreate()`, `SNESSetKSP()`
    5655: @*/
    5656: PetscErrorCode SNESGetKSP(SNES snes, KSP *ksp)
    5657: {
    5658:   PetscFunctionBegin;
    5660:   PetscAssertPointer(ksp, 2);

    5662:   if (!snes->ksp) {
    5663:     PetscCall(KSPCreate(PetscObjectComm((PetscObject)snes), &snes->ksp));
    5664:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->ksp, (PetscObject)snes, 1));

    5666:     PetscCall(KSPSetPreSolve(snes->ksp, KSPPreSolve_SNESEW, snes));
    5667:     PetscCall(KSPSetPostSolve(snes->ksp, KSPPostSolve_SNESEW, snes));

    5669:     PetscCall(KSPMonitorSetFromOptions(snes->ksp, "-snes_monitor_ksp", "snes_preconditioned_residual", snes));
    5670:     PetscCall(PetscObjectSetOptions((PetscObject)snes->ksp, ((PetscObject)snes)->options));
    5671:   }
    5672:   *ksp = snes->ksp;
    5673:   PetscFunctionReturn(PETSC_SUCCESS);
    5674: }

    5676: #include <petsc/private/dmimpl.h>
    5677: /*@
    5678:   SNESSetDM - Sets the `DM` that may be used by some `SNES` nonlinear solvers or their underlying preconditioners

    5680:   Logically Collective

    5682:   Input Parameters:
    5683: + snes - the nonlinear solver context
    5684: - dm   - the `DM`, cannot be `NULL`

    5686:   Level: intermediate

    5688:   Note:
    5689:   A `DM` can only be used for solving one problem at a time because information about the problem is stored on the `DM`,
    5690:   even when not using interfaces like `DMSNESSetFunction()`.  Use `DMClone()` to get a distinct `DM` when solving different
    5691:   problems using the same function space.

    5693: .seealso: [](ch_snes), `DM`, `SNES`, `SNESGetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5694: @*/
    5695: PetscErrorCode SNESSetDM(SNES snes, DM dm)
    5696: {
    5697:   KSP    ksp;
    5698:   DMSNES sdm;

    5700:   PetscFunctionBegin;
    5703:   PetscCall(PetscObjectReference((PetscObject)dm));
    5704:   if (snes->dm) { /* Move the DMSNES context over to the new DM unless the new DM already has one */
    5705:     if (snes->dm->dmsnes && !dm->dmsnes) {
    5706:       PetscCall(DMCopyDMSNES(snes->dm, dm));
    5707:       PetscCall(DMGetDMSNES(snes->dm, &sdm));
    5708:       if (sdm->originaldm == snes->dm) sdm->originaldm = dm; /* Grant write privileges to the replacement DM */
    5709:     }
    5710:     PetscCall(DMCoarsenHookRemove(snes->dm, DMCoarsenHook_SNESVecSol, DMRestrictHook_SNESVecSol, snes));
    5711:     PetscCall(DMDestroy(&snes->dm));
    5712:   }
    5713:   snes->dm     = dm;
    5714:   snes->dmAuto = PETSC_FALSE;

    5716:   PetscCall(SNESGetKSP(snes, &ksp));
    5717:   PetscCall(KSPSetDM(ksp, dm));
    5718:   PetscCall(KSPSetDMActive(ksp, KSP_DMACTIVE_ALL, PETSC_FALSE));
    5719:   if (snes->npc) {
    5720:     PetscCall(SNESSetDM(snes->npc, snes->dm));
    5721:     PetscCall(SNESSetNPCSide(snes, snes->npcside));
    5722:   }
    5723:   PetscFunctionReturn(PETSC_SUCCESS);
    5724: }

    5726: /*@
    5727:   SNESGetDM - Gets the `DM` that may be used by some `SNES` nonlinear solvers/preconditioners

    5729:   Not Collective but `dm` obtained is parallel on `snes`

    5731:   Input Parameter:
    5732: . snes - the `SNES` context

    5734:   Output Parameter:
    5735: . dm - the `DM`

    5737:   Level: intermediate

    5739: .seealso: [](ch_snes), `DM`, `SNES`, `SNESSetDM()`, `KSPSetDM()`, `KSPGetDM()`
    5740: @*/
    5741: PetscErrorCode SNESGetDM(SNES snes, DM *dm)
    5742: {
    5743:   PetscFunctionBegin;
    5745:   if (!snes->dm) {
    5746:     PetscCall(DMShellCreate(PetscObjectComm((PetscObject)snes), &snes->dm));
    5747:     snes->dmAuto = PETSC_TRUE;
    5748:   }
    5749:   *dm = snes->dm;
    5750:   PetscFunctionReturn(PETSC_SUCCESS);
    5751: }

    5753: /*@
    5754:   SNESSetNPC - Sets the nonlinear preconditioner to be used.

    5756:   Collective

    5758:   Input Parameters:
    5759: + snes - iterative context obtained from `SNESCreate()`
    5760: - npc  - the `SNES` nonlinear preconditioner object

    5762:   Options Database Key:
    5763: . -npc_snes_type type - set the type of the `SNES` to use as the nonlinear preconditioner

    5765:   Level: developer

    5767:   Notes:
    5768:   This is rarely used, rather use `SNESGetNPC()` to retrieve the preconditioner and configure it using the API.

    5770:   Only some `SNESType` can use a nonlinear preconditioner

    5772: .seealso: [](ch_snes), `SNES`, `SNESNGS`, `SNESFAS`, `SNESGetNPC()`, `SNESHasNPC()`
    5773: @*/
    5774: PetscErrorCode SNESSetNPC(SNES snes, SNES npc)
    5775: {
    5776:   PetscFunctionBegin;
    5779:   PetscCheckSameComm(snes, 1, npc, 2);
    5780:   PetscCall(PetscObjectReference((PetscObject)npc));
    5781:   PetscCall(SNESDestroy(&snes->npc));
    5782:   snes->npc = npc;
    5783:   PetscFunctionReturn(PETSC_SUCCESS);
    5784: }

    5786: /*@
    5787:   SNESGetNPC - Gets a nonlinear preconditioning solver SNES` to be used to precondition the original nonlinear solver.

    5789:   Not Collective; but any changes to the obtained the `pc` object must be applied collectively

    5791:   Input Parameter:
    5792: . snes - iterative context obtained from `SNESCreate()`

    5794:   Output Parameter:
    5795: . pc - the `SNES` preconditioner context

    5797:   Options Database Key:
    5798: . -npc_snes_type type - set the type of the `SNES` to use as the nonlinear preconditioner

    5800:   Level: advanced

    5802:   Notes:
    5803:   If a `SNES` was previously set with `SNESSetNPC()` then that value is returned, otherwise a new `SNES` object is created that will
    5804:   be used as the nonlinear preconditioner for the current `SNES`.

    5806:   The (preconditioner) `SNES` returned automatically inherits the same nonlinear function and Jacobian supplied to the original
    5807:   `SNES`. These may be overwritten if needed.

    5809:   Use the options database prefixes `-npc_snes`, `-npc_ksp`, etc., to control the configuration of the nonlinear preconditioner

    5811: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESHasNPC()`, `SNES`, `SNESCreate()`
    5812: @*/
    5813: PetscErrorCode SNESGetNPC(SNES snes, SNES *pc)
    5814: {
    5815:   const char *optionsprefix;

    5817:   PetscFunctionBegin;
    5819:   PetscAssertPointer(pc, 2);
    5820:   if (!snes->npc) {
    5821:     PetscCtx ctx;

    5823:     PetscCall(SNESCreate(PetscObjectComm((PetscObject)snes), &snes->npc));
    5824:     PetscCall(PetscObjectIncrementTabLevel((PetscObject)snes->npc, (PetscObject)snes, 1));
    5825:     PetscCall(SNESGetOptionsPrefix(snes, &optionsprefix));
    5826:     PetscCall(SNESSetOptionsPrefix(snes->npc, optionsprefix));
    5827:     PetscCall(SNESAppendOptionsPrefix(snes->npc, "npc_"));
    5828:     if (snes->ops->ctxcompute) {
    5829:       PetscCall(SNESSetComputeApplicationContext(snes, snes->ops->ctxcompute, snes->ops->ctxdestroy));
    5830:     } else {
    5831:       PetscCall(SNESGetApplicationContext(snes, &ctx));
    5832:       PetscCall(SNESSetApplicationContext(snes->npc, ctx));
    5833:     }
    5834:     PetscCall(SNESSetCountersReset(snes->npc, PETSC_FALSE));
    5835:   }
    5836:   *pc = snes->npc;
    5837:   PetscFunctionReturn(PETSC_SUCCESS);
    5838: }

    5840: /*@
    5841:   SNESHasNPC - Returns whether a nonlinear preconditioner is associated with the given `SNES`

    5843:   Not Collective

    5845:   Input Parameter:
    5846: . snes - iterative context obtained from `SNESCreate()`

    5848:   Output Parameter:
    5849: . has_npc - whether the `SNES` has a nonlinear preconditioner or not

    5851:   Level: developer

    5853: .seealso: [](ch_snes), `SNESSetNPC()`, `SNESGetNPC()`
    5854: @*/
    5855: PetscErrorCode SNESHasNPC(SNES snes, PetscBool *has_npc)
    5856: {
    5857:   PetscFunctionBegin;
    5859:   PetscAssertPointer(has_npc, 2);
    5860:   *has_npc = snes->npc ? PETSC_TRUE : PETSC_FALSE;
    5861:   PetscFunctionReturn(PETSC_SUCCESS);
    5862: }

    5864: /*@
    5865:   SNESSetNPCSide - Sets the nonlinear preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5867:   Logically Collective

    5869:   Input Parameter:
    5870: . snes - iterative context obtained from `SNESCreate()`

    5872:   Output Parameter:
    5873: . side - the preconditioning side, where side is one of
    5874: .vb
    5875:       PC_LEFT  - left preconditioning
    5876:       PC_RIGHT - right preconditioning (default for most nonlinear solvers)
    5877: .ve

    5879:   Options Database Key:
    5880: . -snes_npc_side (right|left) - nonlinear preconditioner side

    5882:   Level: intermediate

    5884:   Note:
    5885:   `SNESNRICHARDSON` and `SNESNCG` only support left preconditioning.

    5887: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESNRICHARDSON`, `SNESNCG`, `SNESType`, `SNESGetNPCSide()`, `KSPSetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5888: @*/
    5889: PetscErrorCode SNESSetNPCSide(SNES snes, PCSide side)
    5890: {
    5891:   PetscFunctionBegin;
    5894:   if (side == PC_SIDE_DEFAULT) side = PC_RIGHT;
    5895:   PetscCheck((side == PC_LEFT) || (side == PC_RIGHT), PetscObjectComm((PetscObject)snes), PETSC_ERR_ARG_WRONG, "Only PC_LEFT and PC_RIGHT are supported");
    5896:   snes->npcside = side;
    5897:   PetscFunctionReturn(PETSC_SUCCESS);
    5898: }

    5900: /*@
    5901:   SNESGetNPCSide - Gets the preconditioning side used by the nonlinear preconditioner inside `SNES`.

    5903:   Not Collective

    5905:   Input Parameter:
    5906: . snes - iterative context obtained from `SNESCreate()`

    5908:   Output Parameter:
    5909: . side - the preconditioning side, where side is one of
    5910: .vb
    5911:       `PC_LEFT` - left preconditioning
    5912:       `PC_RIGHT` - right preconditioning (default for most nonlinear solvers)
    5913: .ve

    5915:   Level: intermediate

    5917: .seealso: [](ch_snes), `SNES`, `SNESGetNPC()`, `SNESSetNPCSide()`, `KSPGetPCSide()`, `PC_LEFT`, `PC_RIGHT`, `PCSide`
    5918: @*/
    5919: PetscErrorCode SNESGetNPCSide(SNES snes, PCSide *side)
    5920: {
    5921:   PetscFunctionBegin;
    5923:   PetscAssertPointer(side, 2);
    5924:   *side = snes->npcside;
    5925:   PetscFunctionReturn(PETSC_SUCCESS);
    5926: }

    5928: /*@
    5929:   SNESSetLineSearch - Sets the `SNESLineSearch` to be used for a given `SNES`

    5931:   Collective

    5933:   Input Parameters:
    5934: + snes       - iterative context obtained from `SNESCreate()`
    5935: - linesearch - the linesearch object

    5937:   Level: developer

    5939:   Note:
    5940:   This is almost never used, rather one uses `SNESGetLineSearch()` to retrieve the line search and set options on it
    5941:   to configure it using the API).

    5943: .seealso: [](ch_snes), `SNES`, `SNESLineSearch`, `SNESGetLineSearch()`
    5944: @*/
    5945: PetscErrorCode SNESSetLineSearch(SNES snes, SNESLineSearch linesearch)
    5946: {
    5947:   PetscFunctionBegin;
    5950:   PetscCheckSameComm(snes, 1, linesearch, 2);
    5951:   PetscCall(PetscObjectReference((PetscObject)linesearch));
    5952:   PetscCall(SNESLineSearchDestroy(&snes->linesearch));

    5954:   snes->linesearch = linesearch;
    5955:   PetscFunctionReturn(PETSC_SUCCESS);
    5956: }