static char help[] = "Tests the use of MatSolveTranspose().\n\n";

#include <petscmat.h>

int main(int argc, char **args)
{
  Mat           C, A;
  PetscInt      i, j, m = 5, n = 5, Ii, J;
  PetscScalar   v, five = 5.0, one = 1.0;
  IS            isrow, row, col;
  Vec           x, u, b;
  PetscReal     norm;
  MatFactorInfo info;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-m", &m, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));

  PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, m * n, m * n, 5, NULL, &C));
  PetscCall(MatSetUp(C));

  /* create the matrix for the five point stencil, YET AGAIN*/
  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(ISCreateStride(PETSC_COMM_SELF, (m * n) / 2, 0, 2, &isrow));
  PetscCall(MatZeroRowsIS(C, isrow, five, 0, 0));

  PetscCall(VecCreateSeq(PETSC_COMM_SELF, m * n, &u));
  PetscCall(VecDuplicate(u, &x));
  PetscCall(VecDuplicate(u, &b));
  PetscCall(VecSet(u, one));

  PetscCall(MatMultTranspose(C, u, b));

  /* Set default ordering to be Quotient Minimum Degree; also read
     orderings from the options database */
  PetscCall(MatGetOrdering(C, MATORDERINGQMD, &row, &col));

  PetscCall(MatFactorInfoInitialize(&info));
  PetscCall(MatGetFactor(C, MATSOLVERPETSC, MAT_FACTOR_LU, &A));
  PetscCall(MatLUFactorSymbolic(A, C, row, col, &info));
  PetscCall(MatLUFactorNumeric(A, C, &info));
  PetscCall(MatSolveTranspose(A, b, x));

  PetscCall(ISView(row, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(VecAXPY(x, -1.0, u));
  PetscCall(VecNorm(x, NORM_2, &norm));
  PetscCall(PetscPrintf(PETSC_COMM_SELF, "Norm of error %g\n", (double)norm));

  PetscCall(ISDestroy(&row));
  PetscCall(ISDestroy(&col));
  PetscCall(ISDestroy(&isrow));
  PetscCall(VecDestroy(&u));
  PetscCall(VecDestroy(&x));
  PetscCall(VecDestroy(&b));
  PetscCall(MatDestroy(&C));
  PetscCall(MatDestroy(&A));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:

TEST*/