Date: 2026-03-31T05:46:15+00:00

Actual source code: ex89f.F90

      1: !
      2: !     Creates a tridiagonal sparse matrix explicitly in Fortran and solves a linear system with it
      3: !
      4: !     The matrix is provided in CSR format by the user
      5: !
      6: #include <petsc/finclude/petscksp.h>
      7: program main
      8:   use petscksp
      9:   implicit none

     11:   PetscInt i, n, nz, cnt
     12:   PetscBool flg
     13:   PetscErrorCode ierr
     14:   PetscScalar, pointer :: b(:)

     16:   PetscInt, pointer :: rowptr(:)
     17:   PetscInt, pointer :: colind(:)
     18:   PetscScalar, pointer :: a(:)

     20:   Mat J
     21:   Vec rhs, solution
     22:   KSP ksp

     24:   PetscCallA(PetscInitialize(ierr))

     26:   n = 3
     27:   PetscCallA(PetscOptionsGetInt(PETSC_NULL_OPTIONS, PETSC_NULL_CHARACTER, '-n', n, flg, ierr))
     28:   nz = 3*n - 4

     30:   PetscCallA(VecCreateSeq(PETSC_COMM_SELF, n, rhs, ierr))
     31:   PetscCallA(VecCreateSeq(PETSC_COMM_SELF, n, solution, ierr))
     32:   PetscCallA(PetscShmgetAllocateArrayInt(0_PETSC_INT_KIND, n + 1, rowptr, ierr))
     33:   PetscCallA(PetscShmgetAllocateArrayInt(0_PETSC_INT_KIND, nz, colind, ierr))
     34:   PetscCallA(PetscShmgetAllocateArrayScalar(0_PETSC_INT_KIND, nz, a, ierr))

     36:   PetscCallA(VecGetArray(rhs, b, ierr))
     37:   b(1:n) = 1.0
     38:   PetscCallA(VecRestoreArray(rhs, b, ierr))

     40:   rowptr(0) = 0
     41:   colind(0) = 0
     42:   a(0) = 1.0
     43:   rowptr(1) = 1
     44:   cnt = 1
     45:   do i = 1, n - 2
     46:     colind(cnt) = i - 1
     47:     a(cnt) = -1
     48:     cnt = cnt + 1
     49:     colind(cnt) = i
     50:     a(cnt) = 2
     51:     cnt = cnt + 1
     52:     colind(cnt) = i + 1
     53:     a(cnt) = -1
     54:     cnt = cnt + 1
     55:     rowptr(i + 1) = 3 + rowptr(i)
     56:   end do
     57:   colind(cnt) = n - 1
     58:   a(cnt) = 1.0
     59:   rowptr(n) = cnt + 1

     61:   PetscCallA(MatCreateSeqAIJWithArrays(PETSC_COMM_SELF, n, n, rowptr, colind, a, J, ierr))

     63:   PetscCallA(KSPCreate(PETSC_COMM_SELF, ksp, ierr))
     64:   PetscCallA(KSPSetErrorIfNotConverged(ksp, PETSC_TRUE, ierr))
     65:   PetscCallA(KSPSetFromOptions(ksp, ierr))
     66:   PetscCallA(KSPSetOperators(ksp, J, J, ierr))

     68:   PetscCallA(KSPSolve(ksp, rhs, solution, ierr))

     70: ! Keep the same size and nonzero structure of the matrix but change its numerical entries
     71:   do i = 2, n - 1
     72:     a(2 + 3*(i - 2)) = 4.0
     73:   end do
     74:   PetscCallA(PetscObjectStateIncrease(J, ierr))

     76:   PetscCallA(KSPSolve(ksp, rhs, solution, ierr))

     78:   PetscCallA(KSPDestroy(ksp, ierr))
     79:   PetscCallA(VecDestroy(rhs, ierr))
     80:   PetscCallA(VecDestroy(solution, ierr))
     81:   PetscCallA(MatDestroy(J, ierr))

     83:   PetscCallA(PetscShmgetDeallocateArrayInt(rowptr, ierr))
     84:   PetscCallA(PetscShmgetDeallocateArrayInt(colind, ierr))
     85:   PetscCallA(PetscShmgetDeallocateArrayScalar(a, ierr))
     86:   PetscCallA(PetscFinalize(ierr))
     87: end

     89: !/*TEST
     90: !
     91: !     test:
     92: !       requires: defined(PETSC_USE_SINGLE_LIBRARY)
     93: !       nsize: 3
     94: !       filter: sed 's?ATOL?RTOL?g' | grep -v HERMITIAN | grep -v "shared memory" | grep -v "Mat_0"
     95: !       # use the MPI Linear Solver Server
     96: !       args: -n 20 -mpi_linear_solver_server -mpi_linear_solver_server_view -mpi_linear_solver_server_use_shared_memory false
     97: !       # controls for the use of PCMPI on a particular system
     98: !       args: -mpi_linear_solver_server_minimum_count_per_rank 5 -mpi_linear_solver_server_ksp_view
     99: !       # the usual options for the linear solver (in this case using the server)
    100: !       args: -ksp_monitor -ksp_converged_reason -ksp_view
    101: !
    102: !     test:
    103: !       suffix: 2
    104: !       requires: defined(PETSC_USE_SINGLE_LIBRARY)
    105: !       nsize: 3
    106: !       filter: sed 's?ATOL?RTOL?g' | grep -v HERMITIAN | grep -v "shared memory" | grep -v "Mat_0"
    107: !       # use the MPI Linear Solver Server
    108: !       args: -n 20 -mpi_linear_solver_server -mpi_linear_solver_server_view -mpi_linear_solver_server_use_shared_memory false
    109: !       # controls for the use of PCMPI on a particular system
    110: !       args: -mpi_linear_solver_server_ksp_view
    111: !       # the usual options for the linear solver (in this case using the server)
    112: !       args: -ksp_monitor -ksp_converged_reason -ksp_view
    113: !
    114: !TEST*/