static char help[] = "Saves a dense matrix in a dense format (binary).\n\n";

#include <petscmat.h>

int main(int argc, char **args)
{
  Mat         C;
  PetscScalar v;
  PetscInt    i, j, m = 4, n = 4;
  PetscMPIInt rank, size;
  PetscViewer viewer;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-m", &m, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));

  /* PART 1:  Generate matrix, then write it in binary format */

  /* Generate matrix */
  PetscCall(MatCreateSeqDense(PETSC_COMM_WORLD, m, n, NULL, &C));
  for (i = 0; i < m; i++) {
    for (j = 0; j < n; j++) {
      v = i * m + j;
      PetscCall(MatSetValues(C, 1, &i, 1, &j, &v, INSERT_VALUES));
    }
  }
  PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, "matrix.dat", FILE_MODE_WRITE, &viewer));
  PetscCall(MatView(C, viewer));
  PetscCall(PetscViewerDestroy(&viewer));
  PetscCall(MatDestroy(&C));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
     output_file: output/empty.out

TEST*/