Actual source code: ex12.c


  2: static char help[] = "Demonstrates VecStrideScatter() and VecStrideGather().\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;               /* vectors */
 21:   PetscInt       n   = 20;
 22:   PetscScalar    one = 1.0;

 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,2);
 33:   VecSetFromOptions(v);

 35:   /*
 36:       Create single-component vector
 37:   */
 38:   VecCreate(PETSC_COMM_WORLD,&s);
 39:   VecSetSizes(s,PETSC_DECIDE,n/2);
 40:   VecSetFromOptions(s);

 42:   /*
 43:      Set the vectors to entries to a constant value.
 44:   */
 45:   VecSet(v,one);

 47:   /*
 48:      Get the first component from the multi-component vector to the single vector
 49:   */
 50:   VecStrideGather(v,0,s,INSERT_VALUES);

 52:   VecView(s,PETSC_VIEWER_STDOUT_WORLD);

 54:   /*
 55:      Put the values back into the second component
 56:   */
 57:   VecStrideScatter(s,1,v,ADD_VALUES);

 59:   VecView(v,PETSC_VIEWER_STDOUT_WORLD);

 61:   /*
 62:      Free work space.  All PETSc objects should be destroyed when they
 63:      are no longer needed.
 64:   */
 65:   VecDestroy(&v);
 66:   VecDestroy(&s);
 67:   PetscFinalize();
 68:   return 0;
 69: }

 71: /*TEST

 73:      test:
 74:        nsize: 2

 76: TEST*/