xref: /petsc/src/mat/impls/aij/seq/ij.c (revision 70f55243aafb320636e2a54ff30cab5d1e8d3d7b)

#ifndef lint
static char vcid[] = "$Id: ij.c,v 1.17 1996/03/08 05:47:13 bsmith Exp bsmith $";
#endif

#include "src/mat/impls/aij/seq/aij.h"

/*
  MatToSymmetricIJ_SeqAIJ - Convert a 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 only using
    the lower triangular part of the matrix.

    Input Parameters:
.   Matrix - matrix to convert
.   shiftin - the shift for the original matrix (0 or 1)
.   shiftout - the shift required for the reordering routine (0 or 1)

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

    Notes:
$    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.
*/
int MatToSymmetricIJ_SeqAIJ(int n,int *ai,int *aj,int shiftin, int shiftout,
                            int **iia, int **jja )
{
  int *work,*ia,*ja,*j,i, nz, row, col;

  /* allocate space for row pointers */
  *iia = ia = (int *) PetscMalloc( (n+1)*sizeof(int) ); CHKPTRQ(ia);
  PetscMemzero(ia,(n+1)*sizeof(int));
  work = (int *) PetscMalloc( (n+1)*sizeof(int) ); CHKPTRQ(work);

  /* determine the number of columns in each row */
  ia[0] = -shiftout;
  for (row = 0; row < n; row++) {
    nz = ai[row+1] - ai[row];
    j  = aj + ai[row];
    while (nz--) {
       col = *j++ + shiftin;
       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<n+1; i++ ) {
    row       = ia[i-1];
    ia[i]     += row;
    work[i-1] = row - 1;
  }

  /* allocate space for column pointers */
  nz = ia[n] + (!shiftin);
  *jja = ja = (int *) PetscMalloc( nz*sizeof(int) ); CHKPTRQ(ja);

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