static char help[] = "Tests MPI parallel matrix creation. Test MatCreateRedundantMatrix() \n\n";

#include <petscmat.h>

int main(int argc, char **args)
{
  Mat         C, Credundant;
  MatInfo     info;
  PetscMPIInt rank, size, subsize;
  PetscInt    i, j, m = 3, n = 2, low, high, iglobal;
  PetscInt    Ii, J, ldim, nsubcomms;
  PetscBool   flg_info, flg_mat;
  PetscScalar v, one = 1.0;
  Vec         x, y;
  MPI_Comm    subcomm;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &args, NULL, help));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-m", &m, NULL));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
  n = 2 * size;

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

  /* Create the matrix for the five point stencil, YET AGAIN */
  for (i = 0; i < m; i++) {
    for (j = 2 * rank; j < 2 * rank + 2; 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));
    }
  }

  /* Add extra elements (to illustrate variants of MatGetInfo) */
  Ii = n;
  J  = n - 2;
  v  = 100.0;
  PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));
  Ii = n - 2;
  J  = n;
  v  = 100.0;
  PetscCall(MatSetValues(C, 1, &Ii, 1, &J, &v, INSERT_VALUES));

  PetscCall(MatAssemblyBegin(C, MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(C, MAT_FINAL_ASSEMBLY));

  /* Form vectors */
  PetscCall(MatCreateVecs(C, &x, &y));
  PetscCall(VecGetLocalSize(x, &ldim));
  PetscCall(VecGetOwnershipRange(x, &low, &high));
  for (i = 0; i < ldim; i++) {
    iglobal = i + low;
    v       = one * ((PetscReal)i) + 100.0 * rank;
    PetscCall(VecSetValues(x, 1, &iglobal, &v, INSERT_VALUES));
  }
  PetscCall(VecAssemblyBegin(x));
  PetscCall(VecAssemblyEnd(x));

  PetscCall(MatMult(C, x, y));

  PetscCall(PetscOptionsHasName(NULL, NULL, "-view_info", &flg_info));
  if (flg_info) {
    PetscCall(PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD, PETSC_VIEWER_ASCII_INFO));
    PetscCall(MatView(C, PETSC_VIEWER_STDOUT_WORLD));

    PetscCall(MatGetInfo(C, MAT_GLOBAL_SUM, &info));
    PetscCall(PetscViewerASCIIPrintf(PETSC_VIEWER_STDOUT_WORLD, "matrix information (global sums):\nnonzeros = %" PetscInt_FMT ", allocated nonzeros = %" PetscInt_FMT "\n", (PetscInt)info.nz_used, (PetscInt)info.nz_allocated));
    PetscCall(MatGetInfo(C, MAT_GLOBAL_MAX, &info));
    PetscCall(PetscViewerASCIIPrintf(PETSC_VIEWER_STDOUT_WORLD, "matrix information (global max):\nnonzeros = %" PetscInt_FMT ", allocated nonzeros = %" PetscInt_FMT "\n", (PetscInt)info.nz_used, (PetscInt)info.nz_allocated));
  }

  PetscCall(PetscOptionsHasName(NULL, NULL, "-view_mat", &flg_mat));
  if (flg_mat) PetscCall(MatView(C, PETSC_VIEWER_STDOUT_WORLD));

  /* Test MatCreateRedundantMatrix() */
  nsubcomms = size;
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-nsubcomms", &nsubcomms, NULL));
  PetscCall(MatCreateRedundantMatrix(C, nsubcomms, MPI_COMM_NULL, MAT_INITIAL_MATRIX, &Credundant));
  PetscCall(MatCreateRedundantMatrix(C, nsubcomms, MPI_COMM_NULL, MAT_REUSE_MATRIX, &Credundant));

  PetscCall(PetscObjectGetComm((PetscObject)Credundant, &subcomm));
  PetscCallMPI(MPI_Comm_size(subcomm, &subsize));

  if (subsize == 2 && flg_mat) {
    PetscCall(PetscViewerASCIIPrintf(PETSC_VIEWER_STDOUT_(subcomm), "\n[%d] Credundant:\n", rank));
    PetscCall(MatView(Credundant, PETSC_VIEWER_STDOUT_(subcomm)));
  }
  PetscCall(MatDestroy(&Credundant));

  /* Test MatCreateRedundantMatrix() with user-provided subcomm */
  {
    PetscSubcomm psubcomm;

    PetscCall(PetscSubcommCreate(PETSC_COMM_WORLD, &psubcomm));
    PetscCall(PetscSubcommSetNumber(psubcomm, nsubcomms));
    PetscCall(PetscSubcommSetType(psubcomm, PETSC_SUBCOMM_CONTIGUOUS));
    /* enable runtime switch of psubcomm type, e.g., '-psubcomm_type interlaced */
    PetscCall(PetscSubcommSetFromOptions(psubcomm));

    PetscCall(MatCreateRedundantMatrix(C, nsubcomms, PetscSubcommChild(psubcomm), MAT_INITIAL_MATRIX, &Credundant));
    PetscCall(MatCreateRedundantMatrix(C, nsubcomms, PetscSubcommChild(psubcomm), MAT_REUSE_MATRIX, &Credundant));

    PetscCall(PetscSubcommDestroy(&psubcomm));
    PetscCall(MatDestroy(&Credundant));
  }

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

/*TEST

   test:
      nsize: 3
      args: -view_info

   test:
      suffix: 2
      nsize: 3
      args: -nsubcomms 2 -view_mat -psubcomm_type interlaced

   test:
      suffix: 3
      nsize: 3
      args: -nsubcomms 2 -view_mat -psubcomm_type contiguous

   test:
      suffix: 3_baij
      nsize: 3
      args: -mat_type baij -nsubcomms 2 -view_mat

   test:
      suffix: 3_sbaij
      nsize: 3
      args: -mat_type sbaij -nsubcomms 2 -view_mat

   test:
      suffix: 3_dense
      nsize: 3
      args: -mat_type dense -nsubcomms 2 -view_mat

   test:
      suffix: 4_baij
      nsize: 3
      args: -mat_type baij -nsubcomms 2 -view_mat -psubcomm_type interlaced

   test:
      suffix: 4_sbaij
      nsize: 3
      args: -mat_type sbaij -nsubcomms 2 -view_mat -psubcomm_type interlaced

   test:
      suffix: 4_dense
      nsize: 3
      args: -mat_type dense -nsubcomms 2 -view_mat -psubcomm_type interlaced

TEST*/