#include <petsc.h>

     int main(int argc,char **args)
{
  Vec A,B,C;
  PetscInt   sizeA = 10, m = 8;

     PetscInitialize(&argc,&args,NULL,NULL);

     VecCreate(MPI_COMM_WORLD,&C);
     VecSetSizes(C,PETSC_DECIDE,sizeA+m);
     VecSetFromOptions(C);
     
     VecCreate(MPI_COMM_WORLD,&A);
     VecSetSizes(A,PETSC_DECIDE,sizeA);
     VecSetFromOptions(A);
     
     VecCreate(MPI_COMM_WORLD,&B);
     VecSetSizes(B,PETSC_DECIDE,m);
     VecSetFromOptions(B);
     
     PetscInt start,end;
     IS is_fromA,is_toC1,is_fromB,is_toC2;
     VecScatter scatter1,scatter2;
     
 VecGetOwnershipRange(A,&start,&end);
ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_fromA);
ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_toC1);// this is redundant
VecScatterCreate(A,is_fromA,C,is_toC1,&scatter1);

 VecGetSize(A,&sizeA);
VecGetOwnershipRange(B,&start,&end);
ISCreateStride(MPI_COMM_WORLD,(end-start),start,1,&is_fromB);
ISCreateStride(MPI_COMM_WORLD,(end-start),(start+sizeA),1,&is_toC2); //shifts the index location
VecScatterCreate(B,is_fromB,C,is_toC2,&scatter2);

 VecSetRandom(A,NULL);
 VecView(A,0);
 VecScatterBegin(scatter1,A,C,INSERT_VALUES,SCATTER_FORWARD);
VecScatterEnd(scatter1,A,C,INSERT_VALUES,SCATTER_FORWARD);
 VecView(C,0);
 
VecScatterBegin(scatter1,C,A,INSERT_VALUES,SCATTER_REVERSE);
VecScatterEnd(scatter1,C,A,INSERT_VALUES,SCATTER_REVERSE);
 VecView(A,0);

 PetscFinalize();

 return(0);
}