
static char help[] = "Scatters from a parallel vector into seqential vectors.\n\n";

#include "petscvec.h"
#include "petscsys.h"

#undef __FUNCT__
#define __FUNCT__ "main"
int main(int argc,char **argv)
{
  PetscErrorCode ierr;
  PetscMPIInt    rank;
  PetscInt       n = 5,idx1[2] = {0,3},idx2[2] = {1,4};
  PetscScalar    one = 1.0,two = 2.0;
  Vec            x,y;
  IS             is1,is2;
  VecScatter     ctx = 0;

  ierr = PetscInitialize(&argc,&argv,(char*)0,help);CHKERRQ(ierr); 
  ierr = PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);CHKERRQ(ierr);
  ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRQ(ierr);

  /* create two vectors */
  ierr = VecCreate(PETSC_COMM_WORLD,&x);CHKERRQ(ierr);
  ierr = VecSetSizes(x,n,PETSC_DECIDE);CHKERRQ(ierr);
  ierr = VecSetFromOptions(x);CHKERRQ(ierr);
  ierr = VecCreateSeq(PETSC_COMM_SELF,n,&y);CHKERRQ(ierr);

  /* create two index sets */
  ierr = ISCreateGeneral(PETSC_COMM_SELF,2,idx1,&is1);CHKERRQ(ierr);
  ierr = ISCreateGeneral(PETSC_COMM_SELF,2,idx2,&is2);CHKERRQ(ierr);

  ierr = VecSet(x,one);CHKERRQ(ierr);
  ierr = VecSet(y,two);CHKERRQ(ierr);
  ierr = VecScatterCreate(x,is1,y,is2,&ctx);CHKERRQ(ierr);
  ierr = VecScatterBegin(x,y,INSERT_VALUES,SCATTER_FORWARD,ctx);CHKERRQ(ierr);
  ierr = VecScatterEnd(x,y,INSERT_VALUES,SCATTER_FORWARD,ctx);CHKERRQ(ierr);
  ierr = VecScatterDestroy(ctx);CHKERRQ(ierr);
  
  if (!rank) {VecView(y,PETSC_VIEWER_STDOUT_SELF);CHKERRQ(ierr);}

  ierr = ISDestroy(is1);CHKERRQ(ierr);
  ierr = ISDestroy(is2);CHKERRQ(ierr);

  ierr = VecDestroy(x);CHKERRQ(ierr);
  ierr = VecDestroy(y);CHKERRQ(ierr);
  ierr = PetscFinalize();CHKERRQ(ierr);

  return 0;
}
