graphops/order/spqmd.c

#include <petscmat.h>
#include <petsc/private/matorderimpl.h>

/*
    MatGetOrdering_QMD - Find the Quotient Minimum Degree ordering of a given matrix.
*/
PETSC_INTERN PetscErrorCode MatGetOrdering_QMD(Mat mat, MatOrderingType type, IS *row, IS *col)
{
  PetscInt        i, *deg, *marker, *rchset, *nbrhd, *qsize, *qlink, nofsub, *iperm, nrow, *perm;
  const PetscInt *ia, *ja;
  PetscBool       done;

  PetscFunctionBegin;
  PetscCall(MatGetRowIJ(mat, 1, PETSC_TRUE, PETSC_TRUE, &nrow, &ia, &ja, &done));
  PetscCheck(done, PetscObjectComm((PetscObject)mat), PETSC_ERR_SUP, "Cannot get rows for matrix");

  PetscCall(PetscMalloc1(nrow, &perm));
  PetscCall(PetscMalloc5(nrow, &iperm, nrow, &deg, nrow, &marker, nrow, &rchset, nrow, &nbrhd));
  PetscCall(PetscMalloc2(nrow, &qsize, nrow, &qlink));
  /* WARNING - genqmd trashes ja */
  PetscCall(SPARSEPACKgenqmd(&nrow, ia, ja, perm, iperm, deg, marker, rchset, nbrhd, qsize, qlink, &nofsub));
  PetscCall(MatRestoreRowIJ(mat, 1, PETSC_TRUE, PETSC_TRUE, NULL, &ia, &ja, &done));

  PetscCall(PetscFree2(qsize, qlink));
  PetscCall(PetscFree5(iperm, deg, marker, rchset, nbrhd));
  for (i = 0; i < nrow; i++) perm[i]--;
  PetscCall(ISCreateGeneral(PETSC_COMM_SELF, nrow, perm, PETSC_COPY_VALUES, row));
  PetscCall(ISCreateGeneral(PETSC_COMM_SELF, nrow, perm, PETSC_OWN_POINTER, col));
  PetscFunctionReturn(PETSC_SUCCESS);
}