Actual source code: ex10.c
petsc-3.4.2 2013-07-02

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

      5: #include <petscvec.h>

      9: int main(int argc,char **argv)
     10: {
     12:   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};
     13:   PetscMPIInt    size,rank;
     14:   PetscScalar    value;
     15:   Vec            x,y;
     16:   IS             isx,isy;
     17:   VecScatter     ctx = 0,newctx;

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

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

     25:   PetscOptionsGetInt(NULL,"-bs",&bs,NULL);
     26:   n    = bs*n;

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

     34:   /* create two index sets */
     35:   if (!rank) {
     36:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix0,PETSC_COPY_VALUES,&isx);
     37:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy0,PETSC_COPY_VALUES,&isy);
     38:   } else {
     39:     ISCreateBlock(PETSC_COMM_SELF,bs,3,ix1,PETSC_COPY_VALUES,&isx);
     40:     ISCreateBlock(PETSC_COMM_SELF,bs,3,iy1,PETSC_COPY_VALUES,&isy);
     41:   }

     43:   /* fill local part of parallel vector */
     44:   for (i=n*rank; i<n*(rank+1); i++) {
     45:     value = (PetscScalar) i;
     46:     VecSetValues(x,1,&i,&value,INSERT_VALUES);
     47:   }
     48:   VecAssemblyBegin(x);
     49:   VecAssemblyEnd(x);

     51:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

     53:   /* fill local part of parallel vector */
     54:   for (i=0; i<n; i++) {
     55:     value = -(PetscScalar) (i + 100*rank);
     56:     VecSetValues(y,1,&i,&value,INSERT_VALUES);
     57:   }
     58:   VecAssemblyBegin(y);
     59:   VecAssemblyEnd(y);

     62:   VecScatterCreate(x,isx,y,isy,&ctx);
     63:   VecScatterCopy(ctx,&newctx);
     64:   VecScatterDestroy(&ctx);

     66:   VecScatterBegin(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
     67:   VecScatterEnd(newctx,y,x,INSERT_VALUES,SCATTER_REVERSE);
     68:   VecScatterDestroy(&newctx);

     70:   VecView(x,PETSC_VIEWER_STDOUT_WORLD);

     72:   ISDestroy(&isx);
     73:   ISDestroy(&isy);
     74:   VecDestroy(&x);
     75:   VecDestroy(&y);

     77:   PetscFinalize();
     78:   return 0;
     79: }