2: static char help[]= "Scatters from a parallel vector to a sequential vector.\n\
  3: uses block index sets\n\n";

 5:  #include petsc.h
 6:  #include petscis.h
 7:  #include petscvec.h
 8:  #include petscsys.h

 12: int main(int argc,char **argv)
 13: {
 15:   PetscInt       bs = 1,n = 5,ix0[3] = {5,7,9},ix1[3] = {2,3,4},i,iy0[3] = {1,2,4},iy1[3] = {0,1,3};
 16:   PetscMPIInt    size,rank;
 17:   PetscScalar    value;
 18:   Vec            x,y;
 19:   IS             isx,isy;
 20:   VecScatter     ctx = 0,newctx;

 22:   PetscInitialize(&argc,&argv,(char*)0,help);
 23:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 24:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 26:   if (size != 2) SETERRQ(1,"Must run with 2 processors");

 28:   PetscOptionsGetInt(PETSC_NULL,"-bs",&bs,PETSC_NULL);
 29:   n = bs*n;

 31:   /* create two vectors */
 32:   VecCreate(PETSC_COMM_WORLD,&x);
 33:   VecSetSizes(x,PETSC_DECIDE,size*n);
 34:   VecSetFromOptions(x);
 35:   VecCreateSeq(PETSC_COMM_SELF,n,&y);

 37:   /* create two index sets */
 38:   for (i=0; i<3; i++) {
 39:     ix0[i] *= bs; ix1[i] *= bs;
 40:     iy0[i] *= bs; iy1[i] *= bs;
 41:   }

 43:   if (!rank) {
 44:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix0,&isx);
 45:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy0,&isy);
 46:   } else {
 47:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix1,&isx);
 48:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy1,&isy);
 49:   }

 51:   /* fill local part of parallel vector */
 52:   for (i=n*rank; i<n*(rank+1); i++) {
 53:     value = (PetscScalar) i;
 54:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 55:   }
 56:   VecAssemblyBegin(x);
 57:   VecAssemblyEnd(x);

 59:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

 61:   /* fill local part of parallel vector */
 62:   for (i=0; i<n; i++) {
 63:     value = -(PetscScalar) (i + 100*rank);
 64:     VecSetValues(y,1,&i,&value,INSERT_VALUES);
 65:   }
 66:   VecAssemblyBegin(y);
 67:   VecAssemblyEnd(y);


 70:   VecScatterCreate(x,isx,y,isy,&ctx);
 71:   VecScatterCopy(ctx,&newctx);
 72:   VecScatterDestroy(ctx);

 74:   VecScatterBegin(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
 75:   VecScatterEnd(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
 76:   VecScatterDestroy(newctx);

 78:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

 80:   ISDestroy(isx);
 81:   ISDestroy(isy);
 82:   VecDestroy(x);
 83:   VecDestroy(y);

 85:   PetscFinalize();
 86:   return 0;
 87: }
 88: