Actual source code: ex5.c
2: static char help[] = "Scatters from a parallel vector to a sequential vector.\n\
3: This does case when we are merely selecting the local part of the\n\
4: parallel vector.\n\n";
6: #include <petscvec.h>
8: int main(int argc, char **argv)
9: {
10: PetscMPIInt size, rank;
11: PetscInt n = 5, i;
12: PetscScalar value;
13: Vec x, y;
14: IS is1, is2;
15: VecScatter ctx = 0;
17: PetscFunctionBeginUser;
18: PetscCall(PetscInitialize(&argc, &argv, (char *)0, 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 * size; i++) {
35: value = (PetscScalar)i;
36: PetscCall(VecSetValues(x, 1, &i, &value, INSERT_VALUES));
37: }
38: PetscCall(VecAssemblyBegin(x));
39: PetscCall(VecAssemblyEnd(x));
40: PetscCall(VecView(x, PETSC_VIEWER_STDOUT_WORLD));
42: PetscCall(VecScatterCreate(x, is1, y, is2, &ctx));
43: PetscCall(VecScatterBegin(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD));
44: PetscCall(VecScatterEnd(ctx, x, y, INSERT_VALUES, SCATTER_FORWARD));
45: PetscCall(VecScatterDestroy(&ctx));
47: if (rank == 0) {
48: PetscCall(PetscPrintf(PETSC_COMM_SELF, "----\n"));
49: PetscCall(VecView(y, PETSC_VIEWER_STDOUT_SELF));
50: }
52: PetscCall(VecDestroy(&x));
53: PetscCall(VecDestroy(&y));
54: PetscCall(ISDestroy(&is1));
55: PetscCall(ISDestroy(&is2));
57: PetscCall(PetscFinalize());
58: return 0;
59: }
61: /*TEST
63: test:
64: nsize: 2
66: TEST*/