xref: /petsc/src/mat/impls/aij/seq/ij.c (revision e8e8640d1cb9a3a2f50c0c0d7b26e5c4d521e2e4)

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

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

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

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

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

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

  PetscFunctionBegin;
  /* allocate space for row pointers */
  PetscCall(PetscCalloc1(m + 1, &ia));
  *iia = ia;
  PetscCall(PetscMalloc1(m + 1, &work));

  /* determine the number of columns in each row */
  ia[0] = shiftout;
  for (row = 0; row < m; row++) {
    nz = ai[row + 1] - ai[row];
    j  = aj + ai[row] + shiftin;
    while (nz--) {
      col = *j++ + shiftin;
      if (lower_triangular) {
        if (col > row) break;
      } else {
        if (col < row) break;
      }
      if (col != row) ia[row + 1]++;
      ia[col + 1]++;
    }
  }

  /* shiftin ia[i] to point to next row */
  for (i = 1; i < m + 1; i++) {
    row = ia[i - 1];
    ia[i] += row;
    work[i - 1] = row - shiftout;
  }

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

  /* loop over lower triangular part putting into ja */
  for (row = 0; row < m; row++) {
    nz = ai[row + 1] - ai[row];
    j  = aj + ai[row] + shiftin;
    while (nz--) {
      col = *j++ + shiftin;
      if (lower_triangular) {
        if (col > row) break;
      } else {
        if (col < row) break;
      }
      if (col != row) ja[work[col]++] = row + shiftout;
      ja[work[row]++] = col + shiftout;
    }
  }
  PetscCall(PetscFree(work));
  PetscFunctionReturn(PETSC_SUCCESS);
}