static char help[] = "Tests matrix ordering routines.\n\n";

#include <petscmat.h>
extern PetscErrorCode MatGetOrdering_myordering(Mat, MatOrderingType, IS *, IS *);

int main(int argc, char **args)
{
  Mat                C, Cperm;
  PetscInt           i, j, m = 5, n = 5, Ii, J, ncols;
  PetscScalar        v;
  PetscMPIInt        size;
  IS                 rperm, cperm, icperm;
  const PetscInt    *rperm_ptr, *cperm_ptr, *cols;
  const PetscScalar *vals;
  PetscBool          TestMyorder = PETSC_FALSE;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");

  /* create the matrix for the five point stencil, YET AGAIN */
  PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, m * n, m * n, 5, NULL, &C));
  PetscCall(MatSetUp(C));
  for (i = 0; i < m; i++) {
    for (j = 0; j < n; j++) {
      v  = -1.0;
      Ii = j + n * i;
      if (i > 0) {
        J = Ii - n;
        PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));
      }
      if (i < m - 1) {
        J = Ii + n;
        PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));
      }
      if (j > 0) {
        J = Ii - 1;
        PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));
      }
      if (j < n - 1) {
        J = Ii + 1;
        PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));
      }
      v = 4.0;
      PetscCall(MatSetValues(C, 1, &Ii, 1, &Ii, &v, INSERT_VALUES));
    }
  }
  PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));

  PetscCall(MatGetOrdering(C, MATORDERINGND, &rperm, &cperm));
  PetscCall(ISView(rperm, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(ISDestroy(&rperm));
  PetscCall(ISDestroy(&cperm));

  PetscCall(MatGetOrdering(C, MATORDERINGRCM, &rperm, &cperm));
  PetscCall(ISView(rperm, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(ISDestroy(&rperm));
  PetscCall(ISDestroy(&cperm));

  PetscCall(MatGetOrdering(C, MATORDERINGQMD, &rperm, &cperm));
  PetscCall(ISView(rperm, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(ISDestroy(&rperm));
  PetscCall(ISDestroy(&cperm));

  /* create Cperm = rperm*C*icperm */
  PetscCall(PetscOptionsGetBool(NULL, NULL, "-testmyordering", &TestMyorder, NULL));
  if (TestMyorder) {
    PetscCall(MatGetOrdering_myordering(C, MATORDERINGQMD, &rperm, &cperm));
    printf("myordering's rperm:\n");
    PetscCall(ISView(rperm, PETSC_VIEWER_STDOUT_SELF));
    PetscCall(ISInvertPermutation(cperm, PETSC_DECIDE, &icperm));
    PetscCall(ISGetIndices(rperm, &rperm_ptr));
    PetscCall(ISGetIndices(icperm, &cperm_ptr));
    PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, m * n, m * n, 5, NULL, &Cperm));
    for (i = 0; i < m * n; i++) {
      PetscCall(MatGetRow(C, rperm_ptr[i], &ncols, &cols, &vals));
      for (j = 0; j < ncols; j++) {
        /* printf(" (%d %d %g)\n",i,cperm_ptr[cols[j]],vals[j]); */
        PetscCall(MatSetValues(Cperm, 1, &i, 1, &cperm_ptr[cols[j]], &vals[j], INSERT_VALUES));
      }
    }
    PetscCall(MatAssemblyBegin(Cperm, MAT_FINAL_ASSEMBLY));
    PetscCall(MatAssemblyEnd(Cperm, MAT_FINAL_ASSEMBLY));
    PetscCall(ISRestoreIndices(rperm, &rperm_ptr));
    PetscCall(ISRestoreIndices(icperm, &cperm_ptr));

    PetscCall(ISDestroy(&rperm));
    PetscCall(ISDestroy(&cperm));
    PetscCall(ISDestroy(&icperm));
    PetscCall(MatDestroy(&Cperm));
  }

  PetscCall(MatDestroy(&C));
  PetscCall(PetscFinalize());
  return 0;
}

#include <petsc/private/matimpl.h>
/* This is modified from MatGetOrdering_Natural() */
PetscErrorCode MatGetOrdering_myordering(Mat mat, MatOrderingType type, IS *irow, IS *icol)
{
  PetscInt  n, i, *ii;
  PetscBool done;
  MPI_Comm  comm;

  PetscFunctionBegin;
  PetscCall(PetscObjectGetComm((PetscObject)mat, &comm));
  PetscCall(MatGetRowIJ(mat, 0, PETSC_FALSE, PETSC_TRUE, &n, NULL, NULL, &done));
  PetscCall(MatRestoreRowIJ(mat, 0, PETSC_FALSE, PETSC_TRUE, NULL, NULL, NULL, &done));
  PetscCheck(done, PETSC_COMM_WORLD, PETSC_ERR_SUP, "MatRestoreRowIJ fails!");
  /* matrix may be "compressed" in symbolic factorization, due to i-nodes or block storage */
  PetscCall(PetscMalloc1(n, &ii));
  for (i = 0; i < n; i++) ii[i] = n - i - 1; /* replace your index here */
  PetscCall(ISCreateGeneral(PETSC_COMM_SELF, n, ii, PETSC_COPY_VALUES, irow));
  PetscCall(ISCreateGeneral(PETSC_COMM_SELF, n, ii, PETSC_OWN_POINTER, icol));
  PetscCall(ISSetPermutation(*irow));
  PetscCall(ISSetPermutation(*icol));
  PetscFunctionReturn(PETSC_SUCCESS);
}

/*TEST

   test:

TEST*/