static char help[] = "Scatters from a sequential vector to a parallel vector.\n\
This does the tricky case.\n\n";

#include <petscvec.h>

int main(int argc, char **argv)
{
  PetscInt    n = 5, N;
  PetscMPIInt size, rank;
  PetscScalar value, zero = 0.0;
  Vec         x, y;
  IS          is1, is2;
  VecScatter  ctx = 0;

  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 */
  N = size * n;
  PetscCall(VecCreate(PETSC_COMM_WORLD, &y));
  PetscCall(VecSetSizes(y, PETSC_DECIDE, N));
  PetscCall(VecSetFromOptions(y));
  PetscCall(VecCreateSeq(PETSC_COMM_SELF, N, &x));

  /* create two index sets */
  PetscCall(ISCreateStride(PETSC_COMM_SELF, n, 0, 1, &is1));
  PetscCall(ISCreateStride(PETSC_COMM_SELF, n, rank, 1, &is2));

  value = rank + 1;
  PetscCall(VecSet(x, value));
  PetscCall(VecSet(y, zero));

  PetscCall(VecScatterCreate(x, is1, y, is2, &ctx));
  PetscCall(VecScatterBegin(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterEnd(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
  PetscCall(VecScatterDestroy(&ctx));

  PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(VecDestroy(&x));
  PetscCall(VecDestroy(&y));
  PetscCall(ISDestroy(&is1));
  PetscCall(ISDestroy(&is2));

  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 2

TEST*/
