Actual source code: ex12.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Scatters from a sequential vector to a parallel vector.\n\
      3: This does case when we are merely selecting the local part of the\n\
      4: parallel vector.\n";

      6: #include <petscvec.h>

     10: int main(int argc,char **argv)
     11: {
     13:   PetscMPIInt    size,rank;
     14:   PetscInt       n = 5,i;
     15:   PetscScalar    value;
     16:   Vec            x,y;
     17:   IS             is1,is2;
     18:   VecScatter     ctx = 0;

     20:   PetscInitialize(&argc,&argv,(char*)0,help);

     22:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     23:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     25:   /* create two vectors */
     26:   VecCreate(PETSC_COMM_WORLD,&x);
     27:   VecSetSizes(x,PETSC_DECIDE,size*n);
     28:   VecSetFromOptions(x);
     29:   VecCreateSeq(PETSC_COMM_SELF,n,&y);

     31:   /* create two index sets */
     32:   ISCreateStride(PETSC_COMM_SELF,n,n*rank,1,&is1);
     33:   ISCreateStride(PETSC_COMM_SELF,n,0,1,&is2);

     35:   /* each processor inserts the entire vector */
     36:   /* this is redundant but tests assembly */
     37:   for (i=0; i<n; i++) {
     38:     value = (PetscScalar) (i + 10*rank);
     39:     VecSetValues(y,1,&i,&value,INSERT_VALUES);
     40:   }
     41:   VecAssemblyBegin(y);
     42:   VecAssemblyEnd(y);

     44:   VecScatterCreate(y,is2,x,is1,&ctx);
     45:   VecScatterBegin(ctx,y,x,INSERT_VALUES,SCATTER_FORWARD);
     46:   VecScatterEnd(ctx,y,x,INSERT_VALUES,SCATTER_FORWARD);
     47:   VecScatterDestroy(&ctx);

     49:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

     51:   VecDestroy(&x);
     52:   VecDestroy(&y);
     53:   ISDestroy(&is1);
     54:   ISDestroy(&is2);

     56:   PetscFinalize();
     57:   return 0;
     58: }