static char help[] = "Passes a sparse matrix to MATLAB.\n\n";

#include <petscmat.h>

int main(int argc, char **args)
{
  PetscInt    m = 4, n = 5, i, j, II, J;
  PetscScalar one = 1.0, v;
  Vec         x;
  Mat         A;

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

  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, m * n, m * n));
  PetscCall(MatSetFromOptions(A));
  PetscCall(MatSetUp(A));

  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(A, 1, &II, 1, &J, &v, INSERT_VALUES));
      }
      if (i < m - 1) {
        J = II + n;
        PetscCall(MatSetValues(A, 1, &II, 1, &J, &v, INSERT_VALUES));
      }
      if (j > 0) {
        J = II - 1;
        PetscCall(MatSetValues(A, 1, &II, 1, &J, &v, INSERT_VALUES));
      }
      if (j < n - 1) {
        J = II + 1;
        PetscCall(MatSetValues(A, 1, &II, 1, &J, &v, INSERT_VALUES));
      }
      v = 4.0;
      PetscCall(MatSetValues(A, 1, &II, 1, &II, &v, INSERT_VALUES));
    }
  }
  PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
#if defined(PETSC_USE_SOCKET_VIEWER)
  PetscCall(MatView(A, PETSC_VIEWER_SOCKET_WORLD));
#endif
  PetscCall(VecCreateSeq(PETSC_COMM_SELF, m, &x));
  PetscCall(VecSet(x, one));
#if defined(PETSC_USE_SOCKET_VIEWER)
  PetscCall(VecView(x, PETSC_VIEWER_SOCKET_WORLD));
#endif

  PetscCall(PetscSleep(30));

  PetscCall(VecDestroy(&x));
  PetscCall(MatDestroy(&A));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
     TODO: cannot test with socket viewer

TEST*/