Actual source code: ex12.c

  1: static char help[] = "Scatters from a sequential vector to a parallel vector.\n\
  2: This does case when we are merely selecting the local part of the\n\
  3: parallel vector.\n";

  5: #include <petscvec.h>

  7: int main(int argc, char **argv)
  8: {
  9:   PetscMPIInt size, rank;
 10:   PetscInt    n = 5, i;
 11:   PetscScalar value;
 12:   Vec         x, y;
 13:   IS          is1, is2;
 14:   VecScatter  ctx = 0;

 16:   PetscFunctionBeginUser;
 17:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));

 19:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
 20:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

 22:   /* create two vectors */
 23:   PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
 24:   PetscCall(VecSetSizes(x, PETSC_DECIDE, size * n));
 25:   PetscCall(VecSetFromOptions(x));
 26:   PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &y));

 28:   /* create two index sets */
 29:   PetscCall(ISCreateStride(PETSC_COMM_SELF, n, n * rank, 1, &is1));
 30:   PetscCall(ISCreateStride(PETSC_COMM_SELF, n, 0, 1, &is2));

 32:   /* each processor inserts the entire vector */
 33:   /* this is redundant but tests assembly */
 34:   for (i = 0; i < n; i++) {
 35:     value = (PetscScalar)(i + 10 * rank);
 36:     PetscCall(VecSetValues(y, 1, &i, &value, INSERT_VALUES));
 37:   }
 38:   PetscCall(VecAssemblyBegin(y));
 39:   PetscCall(VecAssemblyEnd(y));

 41:   PetscCall(VecScatterCreate(y, is2, x, is1, &ctx));
 42:   PetscCall(VecScatterBegin(ctx, y, x, INSERT_VALUES, SCATTER_FORWARD));
 43:   PetscCall(VecScatterEnd(ctx, y, x, INSERT_VALUES, SCATTER_FORWARD));
 44:   PetscCall(VecScatterDestroy(&ctx));

 46:   PetscCall(VecView(x, PETSC_VIEWER_STDOUT_WORLD));

 48:   PetscCall(VecDestroy(&x));
 49:   PetscCall(VecDestroy(&y));
 50:   PetscCall(ISDestroy(&is1));
 51:   PetscCall(ISDestroy(&is2));

 53:   PetscCall(PetscFinalize());
 54:   return 0;
 55: }

 57: /*TEST

 59:    test:
 60:       nsize: 2

 62: TEST*/