Actual source code: ex25.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 processor zero is as long as the entire parallel vector; rest are zero length.\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:   if (!rank) {
     29:     VecCreateSeq(PETSC_COMM_SELF,N,&x);
     30:   } else {
     31:     VecCreateSeq(PETSC_COMM_SELF,0,&x);
     32:   }

     34:   /* create two index sets */
     35:   if (!rank) {
     36:     ISCreateStride(PETSC_COMM_SELF,N,0,1,&is1);
     37:     ISCreateStride(PETSC_COMM_SELF,N,0,1,&is2);
     38:   } else {
     39:     ISCreateStride(PETSC_COMM_SELF,0,0,1,&is1);
     40:     ISCreateStride(PETSC_COMM_SELF,0,0,1,&is2);
     41:   }

     43:   VecSet(x,zero);
     44:   VecGetOwnershipRange(y,&low,&high);
     45:   for (i=0; i<n; i++) {
     46:     iglobal = i + low; value = (PetscScalar) (i + 10*rank);
     47:     VecSetValues(y,1,&iglobal,&value,INSERT_VALUES);
     48:   }
     49:   VecAssemblyBegin(y);
     50:   VecAssemblyEnd(y);
     51:   VecView(y,PETSC_VIEWER_STDOUT_WORLD);

     53:   VecScatterCreate(y,is2,x,is1,&ctx);
     54:   VecScatterBegin(ctx,y,x,ADD_VALUES,SCATTER_FORWARD);
     55:   VecScatterEnd(ctx,y,x,ADD_VALUES,SCATTER_FORWARD);
     56:   VecScatterDestroy(&ctx);

     58:   if (!rank) {
     59:     printf("----\n");
     60:     VecView(x,PETSC_VIEWER_STDOUT_SELF);
     61:   }

     63:   VecDestroy(&x);
     64:   VecDestroy(&y);
     65:   ISDestroy(&is1);
     66:   ISDestroy(&is2);

     68:   PetscFinalize();
     69:   return 0;
     70: }