xref: /petsc/src/mat/impls/aij/seq/ij.c (revision 5615d1e584023db9367fb782d85b1b4ebbb8df18)

#ifndef lint
static char vcid[] = "$Id: ij.c,v 1.25 1996/12/17 23:39:44 balay Exp balay $";
#endif

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

#undef __FUNC__
#define __FUNC__ "MatToSymmetricIJ_SeqAIJ"
/*
  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 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 m,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( (m+1)*sizeof(int) ); CHKPTRQ(ia);
  PetscMemzero(ia,(m+1)*sizeof(int));
  work = (int *) PetscMalloc( (m+1)*sizeof(int) ); CHKPTRQ(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 (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);
  *jja = ja = (int *) PetscMalloc( nz*sizeof(int) ); CHKPTRQ(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 (col > row) { break;}
      if (col != row) {ja[work[col]++] = row + shiftout; }
      ja[work[row]++] = col + shiftout;
    }
  }
  PetscFree(work);
  return 0;
}