Date: 2026-03-31T05:46:19+00:00

Actual source code: ij.c

      1: #include <../src/mat/impls/aij/seq/aij.h>

      3: /*
      4:   MatToSymmetricIJ_SeqAIJ - Convert a (generally nonsymmetric) sparse AIJ matrix
      5:            to IJ format (ignore the "A" part) Allocates the space needed. Uses only
      6:            the lower triangular part of the matrix.

      8:     Description:
      9:     Take the data in the row-oriented sparse storage and build the
     10:     IJ data for the Matrix.  Return 0 on success,row + 1 on failure
     11:     at that row. Produces the ij for a symmetric matrix by using
     12:     the lower triangular part of the matrix if lower_triangular is PETSC_TRUE;
     13:     it uses the upper triangular otherwise.

     15:     Input Parameters:
     16: .   Matrix - matrix to convert
     17: .   lower_triangular - symmetrize the lower triangular part
     18: .   shiftin - the shift for the original matrix (0 or 1)
     19: .   shiftout - the shift required for the ordering routine (0 or 1)

     21:     Output Parameters:
     22: .   ia     - ia part of IJ representation (row information)
     23: .   ja     - ja part (column indices)

     25:     Note:
     26:     Both ia and ja may be freed with PetscFree();
     27:     This routine is provided for ordering routines that require a
     28:     symmetric structure.  It is required since those routines call
     29:     SparsePak routines that expect a symmetric  matrix.
     30: */
     31: PetscErrorCode MatToSymmetricIJ_SeqAIJ(PetscInt m, PetscInt *ai, PetscInt *aj, PetscBool lower_triangular, PetscInt shiftin, PetscInt shiftout, PetscInt **iia, PetscInt **jja)
     32: {
     33:   PetscInt *work, *ia, *ja, *j, i, nz, row, col;

     35:   PetscFunctionBegin;
     36:   /* allocate space for row pointers */
     37:   PetscCall(PetscCalloc1(m + 1, &ia));
     38:   *iia = ia;
     39:   PetscCall(PetscMalloc1(m + 1, &work));

     41:   /* determine the number of columns in each row */
     42:   ia[0] = shiftout;
     43:   for (row = 0; row < m; row++) {
     44:     nz = ai[row + 1] - ai[row];
     45:     j  = aj + ai[row] + shiftin;
     46:     while (nz--) {
     47:       col = *j++ + shiftin;
     48:       if (lower_triangular) {
     49:         if (col > row) break;
     50:       } else {
     51:         if (col < row) break;
     52:       }
     53:       if (col != row) ia[row + 1]++;
     54:       ia[col + 1]++;
     55:     }
     56:   }

     58:   /* shiftin ia[i] to point to next row */
     59:   for (i = 1; i < m + 1; i++) {
     60:     row = ia[i - 1];
     61:     ia[i] += row;
     62:     work[i - 1] = row - shiftout;
     63:   }

     65:   /* allocate space for column pointers */
     66:   nz = ia[m] + (!shiftin);
     67:   PetscCall(PetscMalloc1(nz, &ja));
     68:   *jja = ja;

     70:   /* loop over lower triangular part putting into ja */
     71:   for (row = 0; row < m; row++) {
     72:     nz = ai[row + 1] - ai[row];
     73:     j  = aj + ai[row] + shiftin;
     74:     while (nz--) {
     75:       col = *j++ + shiftin;
     76:       if (lower_triangular) {
     77:         if (col > row) break;
     78:       } else {
     79:         if (col < row) break;
     80:       }
     81:       if (col != row) ja[work[col]++] = row + shiftout;
     82:       ja[work[row]++] = col + shiftout;
     83:     }
     84:   }
     85:   PetscCall(PetscFree(work));
     86:   PetscFunctionReturn(PETSC_SUCCESS);
     87: }