static char help[] = "Tests external Clique direct solvers. Simplified from ex130.c\n\
Example: mpiexec -n <np> ./ex168 -f <matrix binary file> \n\n";

#include <petscmat.h>

int main(int argc, char **args)
{
  Mat           A, F;
  Vec           u, x, b;
  PetscMPIInt   rank, size;
  PetscInt      m, n, nfact;
  PetscReal     norm, tol = 1.e-12, Anorm;
  IS            perm, iperm;
  MatFactorInfo info;
  PetscBool     flg, testMatSolve = PETSC_TRUE;
  PetscViewer   fd;                       /* viewer */
  char          file[PETSC_MAX_PATH_LEN]; /* input file name */

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));

  /* Determine file from which we read the matrix A */
  PetscCall(PetscOptionsGetString(NULL, NULL, "-f", file, sizeof(file), &flg));
  PetscCheck(flg, PETSC_COMM_WORLD, PETSC_ERR_USER, "Must indicate binary file with the -f option");

  /* Load matrix A */
  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, file, FILE_MODE_READ, &fd));
  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatLoad(A, fd));
  PetscCall(VecCreate(PETSC_COMM_WORLD, &b));
  PetscCall(VecLoad(b, fd));
  PetscCall(PetscViewerDestroy(&fd));
  PetscCall(MatGetLocalSize(A, &m, &n));
  PetscCheck(m == n, PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "This example is not intended for rectangular matrices (%d, %d)", m, n);
  PetscCall(MatNorm(A, NORM_INFINITY, &Anorm));

  /* Create vectors */
  PetscCall(VecDuplicate(b, &x));
  PetscCall(VecDuplicate(x, &u)); /* save the true solution */

  /* Test Cholesky Factorization */
  PetscCall(MatGetOrdering(A, MATORDERINGNATURAL, &perm, &iperm));

  if (rank == 0) printf(" Clique Cholesky:\n");
  PetscCall(MatGetFactor(A, MATSOLVERCLIQUE, MAT_FACTOR_CHOLESKY, &F));

  info.fill = 5.0;
  PetscCall(MatCholeskyFactorSymbolic(F, A, perm, &info));

  for (nfact = 0; nfact < 1; nfact++) {
    if (rank == 0) printf(" %d-the Cholesky numfactorization \n", nfact);
    PetscCall(MatCholeskyFactorNumeric(F, A, &info));

    /* Test MatSolve() */
    if (testMatSolve && nfact == 2) {
      PetscCall(MatSolve(F, b, x));

      /* Check the residual */
      PetscCall(MatMult(A, x, u));
      PetscCall(VecAXPY(u, -1.0, b));
      PetscCall(VecNorm(u, NORM_INFINITY, &norm));
      /* if (norm > tol) { */
      if (rank == 0) PetscCall(PetscPrintf(PETSC_COMM_SELF, "MatSolve: rel residual %g/%g = %g, LU numfact %d\n", norm, Anorm, norm / Anorm, nfact));
      /*} */
    }
  }

  /* Free data structures */
  PetscCall(MatDestroy(&A));
  PetscCall(MatDestroy(&F));
  PetscCall(ISDestroy(&perm));
  PetscCall(ISDestroy(&iperm));
  PetscCall(VecDestroy(&x));
  PetscCall(VecDestroy(&b));
  PetscCall(VecDestroy(&u));
  PetscCall(PetscFinalize());
  return 0;
}