static char help[] = "Tests the routines VecScatterCreateToAll(), VecScatterCreateToZero()\n\n";

#include <petscvec.h>

int main(int argc, char **argv)
{
  PetscInt    n = 3, i, len, start, end;
  PetscMPIInt size, rank;
  PetscScalar value, *yy;
  Vec         x, y, z, y_t;
  VecScatter  toall, tozero;

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

  /* create two vectors */
  PetscCall(VecCreateFromOptions(PETSC_COMM_WORLD, NULL, 1, PETSC_DECIDE, size * n, &x));

  /* each processor inserts its values */

  PetscCall(VecGetOwnershipRange(x, &start, &end));
  for (i = start; i < end; i++) {
    value = (PetscScalar)i;
    PetscCall(VecSetValues(x, 1, &i, &value, INSERT_VALUES));
  }
  PetscCall(VecAssemblyBegin(x));
  PetscCall(VecAssemblyEnd(x));
  PetscCall(VecView(x, PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(VecScatterCreateToAll(x, &toall, &y));
  PetscCall(VecScatterBegin(toall, x, y, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterEnd(toall, x, y, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterDestroy(&toall));

  /* Cannot view the above vector with VecView(), so place it in an MPI Vec
     and do a VecView() */
  PetscCall(VecGetArray(y, &yy));
  PetscCall(VecGetLocalSize(y, &len));
  PetscCall(VecCreateMPIWithArray(PETSC_COMM_WORLD, 1, len, PETSC_DECIDE, yy, &y_t));
  PetscCall(VecView(y_t, PETSC_VIEWER_STDOUT_WORLD));
  PetscCall(VecDestroy(&y_t));
  PetscCall(VecRestoreArray(y, &yy));

  PetscCall(VecScatterCreateToAll(x, &tozero, &z));
  PetscCall(VecScatterBegin(tozero, x, z, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterEnd(tozero, x, z, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterDestroy(&tozero));
  if (rank == 0) PetscCall(VecView(z, PETSC_VIEWER_STDOUT_SELF));
  PetscCall(VecDestroy(&z));

  PetscCall(VecScatterCreateToZero(x, &tozero, &z));
  PetscCall(VecScatterBegin(tozero, x, z, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterEnd(tozero, x, z, INSERT_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterDestroy(&tozero));
  PetscCall(VecDestroy(&z));

  PetscCall(VecDestroy(&x));
  PetscCall(VecDestroy(&y));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 4

TEST*/
