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

  3: /*
  4:   Include "petscvec.h" so that we can use vectors.  Note that this file
  5:   automatically includes:
  6:      petscsys.h       - base PETSc routines   petscis.h     - index sets
  7:      petscviewer.h - viewers
  8: */

 10: #include <petscvec.h>

 12: int main(int argc, char **argv)
 13: {
 14:   Vec         v, s, r, vecs[2]; /* vectors */
 15:   PetscInt    i, start, end, n = 20;
 16:   PetscScalar value;

 18:   PetscFunctionBeginUser;
 19:   PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
 20:   PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));

 22:   /*
 23:       Create multi-component vector with 2 components
 24:   */
 25:   PetscCall(VecCreate(PETSC_COMM_WORLD, &v));
 26:   PetscCall(VecSetSizes(v, PETSC_DECIDE, n));
 27:   PetscCall(VecSetBlockSize(v, 4));
 28:   PetscCall(VecSetFromOptions(v));

 30:   /*
 31:       Create double-component vectors
 32:   */
 33:   PetscCall(VecCreate(PETSC_COMM_WORLD, &s));
 34:   PetscCall(VecSetSizes(s, PETSC_DECIDE, n / 2));
 35:   PetscCall(VecSetBlockSize(s, 2));
 36:   PetscCall(VecSetFromOptions(s));
 37:   PetscCall(VecDuplicate(s, &r));

 39:   vecs[0] = s;
 40:   vecs[1] = r;
 41:   /*
 42:      Set the vector values
 43:   */
 44:   PetscCall(VecGetOwnershipRange(v, &start, &end));
 45:   for (i = start; i < end; i++) {
 46:     value = i;
 47:     PetscCall(VecSetValues(v, 1, &i, &value, INSERT_VALUES));
 48:   }
 49:   PetscCall(VecAssemblyBegin(v));
 50:   PetscCall(VecAssemblyEnd(v));

 52:   /*
 53:      Get the components from the multi-component vector to the other vectors
 54:   */
 55:   PetscCall(VecStrideGatherAll(v, vecs, INSERT_VALUES));

 57:   PetscCall(VecView(s, PETSC_VIEWER_STDOUT_WORLD));
 58:   PetscCall(VecView(r, PETSC_VIEWER_STDOUT_WORLD));

 60:   PetscCall(VecStrideScatterAll(vecs, v, ADD_VALUES));

 62:   PetscCall(VecView(v, PETSC_VIEWER_STDOUT_WORLD));

 64:   /*
 65:      Free work space.  All PETSc objects should be destroyed when they
 66:      are no longer needed.
 67:   */
 68:   PetscCall(VecDestroy(&v));
 69:   PetscCall(VecDestroy(&s));
 70:   PetscCall(VecDestroy(&r));
 71:   PetscCall(PetscFinalize());
 72:   return 0;
 73: }

 75: /*TEST

 77:      test:
 78:        nsize: 2

 80: TEST*/