Actual source code: ex16.c


  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>

 18: int main(int argc,char **argv)
 19: {
 20:   Vec            v,s,r,vecs[2];               /* vectors */
 21:   PetscInt       i,start,end,n = 20;
 22:   PetscScalar    value;

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

 27:   /*
 28:       Create multi-component vector with 2 components
 29:   */
 30:   VecCreate(PETSC_COMM_WORLD,&v);
 31:   VecSetSizes(v,PETSC_DECIDE,n);
 32:   VecSetBlockSize(v,4);
 33:   VecSetFromOptions(v);

 35:   /*
 36:       Create double-component vectors
 37:   */
 38:   VecCreate(PETSC_COMM_WORLD,&s);
 39:   VecSetSizes(s,PETSC_DECIDE,n/2);
 40:   VecSetBlockSize(s,2);
 41:   VecSetFromOptions(s);
 42:   VecDuplicate(s,&r);

 44:   vecs[0] = s;
 45:   vecs[1] = r;
 46:   /*
 47:      Set the vector values
 48:   */
 49:   VecGetOwnershipRange(v,&start,&end);
 50:   for (i=start; i<end; i++) {
 51:     value = i;
 52:     VecSetValues(v,1,&i,&value,INSERT_VALUES);
 53:   }

 55:   /*
 56:      Get the components from the multi-component vector to the other vectors
 57:   */
 58:   VecStrideGatherAll(v,vecs,INSERT_VALUES);

 60:   VecView(s,PETSC_VIEWER_STDOUT_WORLD);
 61:   VecView(r,PETSC_VIEWER_STDOUT_WORLD);

 63:   VecStrideScatterAll(vecs,v,ADD_VALUES);

 65:   VecView(v,PETSC_VIEWER_STDOUT_WORLD);

 67:   /*
 68:      Free work space.  All PETSc objects should be destroyed when they
 69:      are no longer needed.
 70:   */
 71:   VecDestroy(&v);
 72:   VecDestroy(&s);
 73:   VecDestroy(&r);
 74:   PetscFinalize();
 75:   return 0;
 76: }

 78: /*TEST

 80:      test:
 81:        nsize: 2

 83: TEST*/