Actual source code: ex16.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Demonstrates VecStrideScatter() and VecStrideGather() with subvectors that are also strided.\n\n";

      4: /*T
      5:    Concepts: vectors^sub-vectors;
      6:    Processors: n
      7: T*/

      9: /*
     10:   Include "petscvec.h" so that we can use vectors.  Note that this file
     11:   automatically includes:
     12:      petscsys.h       - base PETSc routines   petscis.h     - index sets
     13:      petscviewer.h - viewers
     14: */

     16: #include <petscvec.h>

     20: int main(int argc,char **argv)
     21: {
     22:   Vec            v,s,r,vecs[2];               /* vectors */
     23:   PetscInt       i,start,end,n = 20;
     25:   PetscScalar    value;

     27:   PetscInitialize(&argc,&argv,(char*)0,help);
     28:   PetscOptionsGetInt(NULL,"-n",&n,NULL);

     30:   /*
     31:       Create multi-component vector with 2 components
     32:   */
     33:   VecCreate(PETSC_COMM_WORLD,&v);
     34:   VecSetSizes(v,PETSC_DECIDE,n);
     35:   VecSetBlockSize(v,4);
     36:   VecSetFromOptions(v);

     38:   /*
     39:       Create double-component vectors
     40:   */
     41:   VecCreate(PETSC_COMM_WORLD,&s);
     42:   VecSetSizes(s,PETSC_DECIDE,n/2);
     43:   VecSetBlockSize(s,2);
     44:   VecSetFromOptions(s);
     45:   VecDuplicate(s,&r);

     47:   vecs[0] = s;
     48:   vecs[1] = r;
     49:   /*
     50:      Set the vector values
     51:   */
     52:   VecGetOwnershipRange(v,&start,&end);
     53:   for (i=start; i<end; i++) {
     54:     value = i;
     55:     VecSetValues(v,1,&i,&value,INSERT_VALUES);
     56:   }

     58:   /*
     59:      Get the components from the multi-component vector to the other vectors
     60:   */
     61:   VecStrideGatherAll(v,vecs,INSERT_VALUES);

     63:   VecView(s,PETSC_VIEWER_STDOUT_WORLD);
     64:   VecView(r,PETSC_VIEWER_STDOUT_WORLD);

     66:   VecStrideScatterAll(vecs,v,ADD_VALUES);

     68:   VecView(v,PETSC_VIEWER_STDOUT_WORLD);

     70:   /*
     71:      Free work space.  All PETSc objects should be destroyed when they
     72:      are no longer needed.
     73:   */
     74:   VecDestroy(&v);
     75:   VecDestroy(&s);
     76:   VecDestroy(&r);
     77:   PetscFinalize();
     78:   return 0;
     79: }