#include "petsc.h"
#include "petscvec.h"
#include "petscda.h"

static char help[] = "Test on vecscattertozero\n\n";






int main(int argc,char **argv)
{
VecScatter   ctx;
DA da;
int nx, ny, i, j, ij;
Vec coords, scoords;
int rank;
PetscInitialize(&argc,&argv,(char *)0,help);


nx =  5;
ny =  5;


DACreate2d( PETSC_COMM_WORLD          ,  // MPI Communicator
            DA_NONPERIODIC            ,  // The grid is non periodic
            DA_STENCIL_STAR           ,  // choose the appropriate stencil
            nx ,ny                    ,  // global dimension in each direction of the array 
            PETSC_DECIDE,PETSC_DECIDE ,  // let petsc decide what are the LOCAL dimensions on each processors
            3                         ,  // number of degree of freedom per node
            1                         ,  // stencil width (for ghost points)
            PETSC_NULL, PETSC_NULL    ,  // let it null
            &da);                        // the DA to be created.


DASetUniformCoordinates(da  ,                 // the DA
                        0.0 ,                 // x0
                        1.0,                  // xmax
                        0.0,                  // y0
                        1.0,                  // ymax
                        0.0, 0.0);            // z0 and zmax are null because 2D

DAGetCoordinates(da, &coords);                // put these coord. in a global vector


VecCreateSeq(PETSC_COMM_SELF, nx*ny*2, &scoords);                        
VecScatterCreateToZero(coords, &ctx, &scoords);                           
VecScatterBegin(ctx,coords,scoords,INSERT_VALUES,SCATTER_FORWARD);
VecScatterEnd(ctx,coords,scoords,INSERT_VALUES,SCATTER_FORWARD);


MPI_Comm_rank(PETSC_COMM_WORLD, &rank);

VecView(coords, PETSC_VIEWER_STDOUT_WORLD);
PetscPrintf(PETSC_COMM_WORLD, "\n\n");
VecView(scoords, PETSC_VIEWER_STDOUT_SELF);


DADestroy(da);
VecDestroy(coords);


PetscFinalize();

return 0;
}