
static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
Tests where the local part of the scatter is a copy.\n\n";

#include <petscvec.h>

#undef __FUNCT__
#define __FUNCT__ "main"
int main(int argc,char **argv)
{
  PetscErrorCode ierr;
  PetscMPIInt    size,rank;
  PetscInt       n = 5,i,*blks,bs = 1,m = 2;
  PetscScalar    value;
  Vec            x,y;
  IS             is1,is2;
  VecScatter     ctx = 0;
  PetscViewer    sviewer;

  ierr = PetscInitialize(&argc,&argv,(char*)0,help);CHKERRQ(ierr);

  ierr = PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsGetInt(NULL,NULL,"-bs",&bs,NULL);CHKERRQ(ierr);

  ierr = MPI_Comm_size(PETSC_COMM_WORLD,&size);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,PETSC_DECIDE,size*bs*n);CHKERRQ(ierr);
  ierr = VecSetFromOptions(x);CHKERRQ(ierr);

  /* create two index sets */
  if (rank < size-1) m = n + 2;
  else m = n;

  ierr = PetscMalloc1(m,&blks);CHKERRQ(ierr);
  blks[0] = n*rank;
  for (i=1; i<m; i++) blks[i] = blks[i-1] + 1;
  ierr = ISCreateBlock(PETSC_COMM_SELF,bs,m,blks,PETSC_COPY_VALUES,&is1);CHKERRQ(ierr);
  ierr = PetscFree(blks);CHKERRQ(ierr);

  ierr = VecCreateSeq(PETSC_COMM_SELF,bs*m,&y);CHKERRQ(ierr);
  ierr = ISCreateStride(PETSC_COMM_SELF,bs*m,0,1,&is2);CHKERRQ(ierr);

  /* each processor inserts the entire vector */
  /* this is redundant but tests assembly */
  for (i=0; i<bs*n*size; i++) {
    value = (PetscScalar) i;
    ierr  = VecSetValues(x,1,&i,&value,INSERT_VALUES);CHKERRQ(ierr);
  }
  ierr = VecAssemblyBegin(x);CHKERRQ(ierr);
  ierr = VecAssemblyEnd(x);CHKERRQ(ierr);
  ierr = VecView(x,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);

  ierr = VecScatterCreate(x,is1,y,is2,&ctx);CHKERRQ(ierr);
  ierr = VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr);
  ierr = VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr);

  ierr = PetscViewerASCIIPushSynchronized(PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  ierr = PetscViewerASCIISynchronizedPrintf(PETSC_VIEWER_STDOUT_WORLD,"----\n");CHKERRQ(ierr);
  ierr = PetscViewerGetSubViewer(PETSC_VIEWER_STDOUT_WORLD,PETSC_COMM_SELF,&sviewer);CHKERRQ(ierr);
  ierr = VecView(y,sviewer);CHKERRQ(ierr); fflush(stdout);
  ierr = PetscViewerRestoreSubViewer(PETSC_VIEWER_STDOUT_WORLD,PETSC_COMM_SELF,&sviewer);CHKERRQ(ierr);
  ierr = PetscViewerFlush(PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  ierr = PetscViewerASCIIPopSynchronized(PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);

  ierr = VecScatterDestroy(&ctx);CHKERRQ(ierr);

  ierr = VecDestroy(&x);CHKERRQ(ierr);
  ierr = VecDestroy(&y);CHKERRQ(ierr);
  ierr = ISDestroy(&is1);CHKERRQ(ierr);
  ierr = ISDestroy(&is2);CHKERRQ(ierr);

  ierr = PetscFinalize();
  return 0;
}

