Actual source code: ex17.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Scatters from a parallel vector to a sequential vector.  In\n\
      3: this case each local vector is as long as the entire parallel vector.\n\n";

      5: #include <petscvec.h>

      9: int main(int argc,char **argv)
     10: {
     12:   PetscInt       n = 5,N,low,high,iglobal,i;
     13:   PetscMPIInt    size,rank;
     14:   PetscScalar    value,zero = 0.0;
     15:   Vec            x,y;
     16:   IS             is1,is2;
     17:   VecScatter     ctx;

     19:   PetscInitialize(&argc,&argv,(char*)0,help);
     20:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     21:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

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

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

     34:   VecSet(x,zero);
     35:   VecGetOwnershipRange(y,&low,&high);
     36:   for (i=0; i<n; i++) {
     37:     iglobal = i + low; value = (PetscScalar) (i + 10*rank);
     38:     VecSetValues(y,1,&iglobal,&value,INSERT_VALUES);
     39:   }
     40:   VecAssemblyBegin(y);
     41:   VecAssemblyEnd(y);
     42:   VecView(y,PETSC_VIEWER_STDOUT_WORLD);

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

     49:   if (!rank) {
     50:     printf("----\n");
     51:     VecView(x,PETSC_VIEWER_STDOUT_SELF);
     52:   }

     54:   VecDestroy(&x);
     55:   VecDestroy(&y);
     56:   ISDestroy(&is1);
     57:   ISDestroy(&is2);

     59:   PetscFinalize();
     60:   return 0;
     61: }