static char help[] = "Tests binary I/O of matrices and illustrates user-defined event logging.\n\n";

#include <petscmat.h>

/* Note:  Most applications would not read and write the same matrix within
  the same program.  This example is intended only to demonstrate
  both input and output. */

int main(int argc, char **args)
{
  Mat           C;
  PetscScalar   v;
  PetscInt      i, j, Ii, J, Istart, Iend, N, m = 4, n = 4;
  PetscMPIInt   rank, size;
  PetscViewer   viewer;
  PetscLogEvent MATRIX_GENERATE, MATRIX_READ;

  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));
  N = m * n;

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

  PetscCall(PetscLogEventRegister("Generate Matrix", 0, &MATRIX_GENERATE));
  PetscCall(PetscLogEventBegin(MATRIX_GENERATE, 0, 0, 0, 0));

  /* Generate matrix */
  PetscCall(MatCreate(PETSC_COMM_WORLD, &C));
  PetscCall(MatSetSizes(C, PETSC_DECIDE, PETSC_DECIDE, N, N));
  PetscCall(MatSetFromOptions(C));
  PetscCall(MatSetUp(C));
  PetscCall(MatGetOwnershipRange(C, &Istart, &Iend));
  for (Ii = Istart; Ii < Iend; Ii++) {
    v = -1.0;
    i = Ii / n;
    j = Ii - i * n;
    if (i > 0) {
      J = Ii - n;
      PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, ADD_VALUES));
    }
    if (i < m - 1) {
      J = Ii + n;
      PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, ADD_VALUES));
    }
    if (j > 0) {
      J = Ii - 1;
      PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, ADD_VALUES));
    }
    if (j < n - 1) {
      J = Ii + 1;
      PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, ADD_VALUES));
    }
    v = 4.0;
    PetscCall(MatSetValues(C, 1, &Ii, 1, &Ii, &v, ADD_VALUES));
  }
  PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));
  PetscCall(MatView(C, PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "writing matrix in binary to matrix.dat ...\n"));
  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, "matrix.dat", FILE_MODE_WRITE, &viewer));
  PetscCall(MatView(C, viewer));
  PetscCall(PetscViewerDestroy(&viewer));
  PetscCall(MatDestroy(&C));
  PetscCall(PetscLogEventEnd(MATRIX_GENERATE, 0, 0, 0, 0));

  /* PART 2:  Read in matrix in binary format */

  /* All processors wait until test matrix has been dumped */
  PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));

  PetscCall(PetscLogEventRegister("Read Matrix", 0, &MATRIX_READ));
  PetscCall(PetscLogEventBegin(MATRIX_READ, 0, 0, 0, 0));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD, "reading matrix in binary from matrix.dat ...\n"));
  PetscCall(PetscViewerBinaryOpen(PETSC_COMM_WORLD, "matrix.dat", FILE_MODE_READ, &viewer));
  PetscCall(MatCreate(PETSC_COMM_WORLD, &C));
  PetscCall(MatLoad(C, viewer));
  PetscCall(PetscViewerDestroy(&viewer));
  PetscCall(PetscLogEventEnd(MATRIX_READ, 0, 0, 0, 0));
  PetscCall(MatView(C, PETSC_VIEWER_STDOUT_WORLD));

  /* Free data structures */
  PetscCall(MatDestroy(&C));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      filter: grep -v " MPI process"

TEST*/