static char help[] = "Tests setup PCFIELDSPLIT with blocked IS.\n\n";
/*
 Contributed by Hoang Giang Bui, June 2017.
 */
#include <petscksp.h>

int main(int argc, char *argv[])
{
  Mat         A;
  KSP         ksp;
  PC          pc;
  PetscInt    Istart, Iend, local_m, local_n, i;
  PetscMPIInt rank;
  PetscInt    method = 2, mat_size = 40, block_size = 2, *A_indices = NULL, *B_indices = NULL, A_size = 0, B_size = 0;
  IS          A_IS, B_IS;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
  PetscCallMPI(MPI_Comm_rank(MPI_COMM_WORLD, &rank));

  PetscCall(PetscOptionsGetInt(NULL, NULL, "-mat_size", &mat_size, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-method", &method, NULL));
  PetscCall(PetscOptionsGetInt(NULL, NULL, "-block_size", &block_size, NULL));

  if (rank == 0) PetscCall(PetscPrintf(PETSC_COMM_SELF, "  matrix size = %" PetscInt_FMT ", block size = %" PetscInt_FMT "\n", mat_size, block_size));

  PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
  PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, mat_size, mat_size));
  PetscCall(MatSetType(A, MATMPIAIJ));
  PetscCall(MatSetUp(A));

  PetscCall(MatGetOwnershipRange(A, &Istart, &Iend));

  for (i = Istart; i < Iend; ++i) {
    PetscCall(MatSetValue(A, i, i, 2, INSERT_VALUES));
    if (i < mat_size - 1) PetscCall(MatSetValue(A, i, i + 1, -1, INSERT_VALUES));
    if (i > 0) PetscCall(MatSetValue(A, i, i - 1, -1, INSERT_VALUES));
  }

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

  PetscCall(MatGetLocalSize(A, &local_m, &local_n));

  /* Create Index Sets */
  if (rank == 0) {
    if (method > 1) {
      /* with method > 1, the fieldsplit B is set to zero */
      A_size = Iend - Istart;
      B_size = 0;
    } else {
      /* with method = 1, the fieldsplit A and B is equal. It is noticed that A_size, or N/4, must be divided by block_size */
      A_size = (Iend - Istart) / 2;
      B_size = (Iend - Istart) / 2;
    }
    PetscCall(PetscCalloc1(A_size, &A_indices));
    PetscCall(PetscCalloc1(B_size, &B_indices));
    for (i = 0; i < A_size; ++i) A_indices[i] = Istart + i;
    for (i = 0; i < B_size; ++i) B_indices[i] = Istart + i + A_size;
  } else if (rank == 1) {
    A_size = (Iend - Istart) / 2;
    B_size = (Iend - Istart) / 2;
    PetscCall(PetscCalloc1(A_size, &A_indices));
    PetscCall(PetscCalloc1(B_size, &B_indices));
    for (i = 0; i < A_size; ++i) A_indices[i] = Istart + i;
    for (i = 0; i < B_size; ++i) B_indices[i] = Istart + i + A_size;
  }

  PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, A_size, A_indices, PETSC_OWN_POINTER, &A_IS));
  PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, B_size, B_indices, PETSC_OWN_POINTER, &B_IS));
  PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d]: A_size = %" PetscInt_FMT ", B_size = %" PetscInt_FMT "\n", rank, A_size, B_size));
  PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));

  /* Solve the system */
  PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
  PetscCall(KSPSetType(ksp, KSPGMRES));
  PetscCall(KSPSetOperators(ksp, A, A));

  /* Define the fieldsplit for the global matrix */
  PetscCall(KSPGetPC(ksp, &pc));
  PetscCall(PCSetType(pc, PCFIELDSPLIT));
  PetscCall(PCFieldSplitSetIS(pc, "a", A_IS));
  PetscCall(PCFieldSplitSetIS(pc, "b", B_IS));
  PetscCall(ISSetBlockSize(A_IS, block_size));
  PetscCall(ISSetBlockSize(B_IS, block_size));

  PetscCall(KSPSetFromOptions(ksp));
  PetscCall(KSPSetUp(ksp));

  PetscCall(ISDestroy(&A_IS));
  PetscCall(ISDestroy(&B_IS));
  PetscCall(KSPDestroy(&ksp));
  PetscCall(MatDestroy(&A));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 2
      args: -method 1

   test:
      suffix: 2
      nsize: 2
      args: -method 2

TEST*/
