Actual source code: ex5.c
1: static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
2: This does case when we are merely selecting the local part of the\n\
3: parallel vector.\n\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, (char *)0, help));
18: PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
19: PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
21: /* create two vectors */
22: PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
23: PetscCall(VecSetSizes(x, PETSC_DECIDE, size * n));
24: PetscCall(VecSetFromOptions(x));
25: PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &y));
27: /* create two index sets */
28: PetscCall(ISCreateStride(PETSC_COMM_SELF, n, n * rank, 1, &is1));
29: PetscCall(ISCreateStride(PETSC_COMM_SELF, n, 0, 1, &is2));
31: /* each processor inserts the entire vector */
32: /* this is redundant but tests assembly */
33: for (i = 0; i < n * size; i++) {
34: value = (PetscScalar)i;
35: PetscCall(VecSetValues(x, 1, &i, &value, INSERT_VALUES));
36: }
37: PetscCall(VecAssemblyBegin(x));
38: PetscCall(VecAssemblyEnd(x));
39: PetscCall(VecView(x, PETSC_VIEWER_STDOUT_WORLD));
41: PetscCall(VecScatterCreate(x, is1, y, is2, &ctx));
42: PetscCall(VecScatterBegin(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD));
43: PetscCall(VecScatterEnd(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD));
44: PetscCall(VecScatterDestroy(&ctx));
46: if (rank == 0) {
47: PetscCall(PetscPrintf(PETSC_COMM_SELF, "----\n"));
48: PetscCall(VecView(y, PETSC_VIEWER_STDOUT_SELF));
49: }
51: PetscCall(VecDestroy(&x));
52: PetscCall(VecDestroy(&y));
53: PetscCall(ISDestroy(&is1));
54: PetscCall(ISDestroy(&is2));
56: PetscCall(PetscFinalize());
57: return 0;
58: }
60: /*TEST
62: test:
63: nsize: 2
65: TEST*/