Actual source code: ex9.c
 
   petsc-3.7.7 2017-09-25
   
  2: static char help[]= "Scatters from a parallel vector to a sequential vector.\n\n";
  4: #include <petscvec.h>
  8: int main(int argc,char **argv)
  9: {
 11:   PetscInt       n = 5,i,idx2[3] = {0,2,3},idx1[3] = {0,1,2};
 12:   PetscMPIInt    size,rank;
 13:   PetscScalar    value;
 14:   Vec            x,y;
 15:   IS             is1,is2;
 16:   VecScatter     ctx = 0;
 18:   PetscInitialize(&argc,&argv,(char*)0,help);
 19:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 20:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 22:   /* create two vectors */
 23:   VecCreate(PETSC_COMM_WORLD,&x);
 24:   VecSetSizes(x,PETSC_DECIDE,size*n);
 25:   VecSetFromOptions(x);
 26:   VecCreateSeq(PETSC_COMM_SELF,n,&y);
 28:   /* create two index sets */
 29:   ISCreateGeneral(PETSC_COMM_SELF,3,idx1,PETSC_COPY_VALUES,&is1);
 30:   ISCreateGeneral(PETSC_COMM_SELF,3,idx2,PETSC_COPY_VALUES,&is2);
 32:   /* fill local part of parallel vector */
 33:   for (i=n*rank; i<n*(rank+1); i++) {
 34:     value = (PetscScalar) i;
 35:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
 36:   }
 37:   VecAssemblyBegin(x);
 38:   VecAssemblyEnd(x);
 40:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);
 42:   VecSet(y,-1.0);
 44:   VecScatterCreate(x,is1,y,is2,&ctx);
 45:   VecScatterBegin(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 46:   VecScatterEnd(ctx,x,y,INSERT_VALUES,SCATTER_FORWARD);
 47:   VecScatterDestroy(&ctx);
 49:   if (!rank) {
 50:     PetscPrintf(PETSC_COMM_SELF,"scattered vector\n");
 51:     VecView(y,PETSC_VIEWER_STDOUT_SELF);
 52:   }
 53:   ISDestroy(&is1);
 54:   ISDestroy(&is2);
 55:   VecDestroy(&x);
 56:   VecDestroy(&y);
 58:   PetscFinalize();
 59:   return 0;
 60: }