[petsc-users] VecRestoreSubVector can't change value of original vector

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Hello,

I have a vector(v). I use VecRestoreSubVector to get a sub vector(subv). 
I change the value of the sub vector and want to give the new value back 
to v using VecRestoreSubVector, but it only works for seqential 
case(mpirun -np 1 ...). This is my code. Thank you very much.

#include "petsc.h"
#include "mpi.h"

int main(int argc, char** argv){

   PetscInitialize(&argc,&argv,0,0);

   int commSize;
   int commRank;
   MPI_Comm_rank(MPI_COMM_WORLD,&commRank);
   MPI_Comm_size(MPI_COMM_WORLD,&commSize);

   Vec v;
   VecCreateMPI(PETSC_COMM_WORLD,5,5*commSize,&v);
   VecSet(v,0.0);
   VecAssemblyBegin(v);
   VecAssemblyEnd(v);

   // is
   IS is;
   int index[1], Nindex = 1;
   index[0] = 0;
ISCreateGeneral(PETSC_COMM_WORLD,Nindex,index,PETSC_COPY_VALUES,&is);

   Vec vsub;
   VecGetSubVector(v,is,&vsub);
   VecSet(vsub,1);
   VecAssemblyBegin(vsub);
   VecAssemblyEnd(vsub);

   // VecView(vsub,PETSC_VIEWER_STDOUT_WORLD);

   VecRestoreSubVector(v,is,&vsub);
   // VecAssemblyBegin(v);
   // VecAssemblyEnd(v);

   VecView(v,PETSC_VIEWER_STDOUT_WORLD);

   PetscFinalize();

   return 0;
}

Regards,

fxing