Actual source code: ex16.c
petsc-3.13.6 2020-09-29
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      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;
     23:   PetscScalar    value;

     25:   PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
     26:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);

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

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

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

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

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

     64:   VecStrideScatterAll(vecs,v,ADD_VALUES);

     66:   VecView(v,PETSC_VIEWER_STDOUT_WORLD);

     68:   /*
     69:      Free work space.  All PETSc objects should be destroyed when they
     70:      are no longer needed.
     71:   */
     72:   VecDestroy(&v);
     73:   VecDestroy(&s);
     74:   VecDestroy(&r);
     75:   PetscFinalize();
     76:   return ierr;
     77: }

     79: /*TEST

     81:      test:
     82:        nsize: 2

     84: TEST*/