Actual source code: ex17.c
1: static char help[] = "Scatters from a parallel vector to a sequential vector. In\n\
2: this case each local vector is as long as the entire parallel vector.\n\n";
4: #include <petscvec.h>
6: int main(int argc, char **argv)
7: {
8: PetscInt n = 5, N, low, high, iglobal, i;
9: PetscMPIInt size, rank;
10: PetscScalar value, zero = 0.0;
11: Vec x, y;
12: IS is1, is2;
13: VecScatter ctx;
15: PetscFunctionBeginUser;
16: PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
17: PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
18: PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
20: /* create two vectors */
21: N = size * n;
22: PetscCall(VecCreate(PETSC_COMM_WORLD, &y));
23: PetscCall(VecSetSizes(y, PETSC_DECIDE, N));
24: PetscCall(VecSetFromOptions(y));
25: PetscCall(VecCreateSeq(PETSC_COMM_SELF, N, &x));
27: /* create two index sets */
28: PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is1));
29: PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is2));
31: PetscCall(VecSet(x, zero));
32: PetscCall(VecGetOwnershipRange(y, &low, &high));
33: for (i = 0; i < n; i++) {
34: iglobal = i + low;
35: value = (PetscScalar)(i + 10 * rank);
36: PetscCall(VecSetValues(y, 1, &iglobal, &value, INSERT_VALUES));
37: }
38: PetscCall(VecAssemblyBegin(y));
39: PetscCall(VecAssemblyEnd(y));
40: PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));
42: PetscCall(VecScatterCreate(y, is2, x, is1, &ctx));
43: PetscCall(VecScatterBegin(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
44: PetscCall(VecScatterEnd(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
45: PetscCall(VecScatterDestroy(&ctx));
47: if (rank == 0) {
48: PetscCall(PetscPrintf(PETSC_COMM_SELF, "----\n"));
49: PetscCall(VecView(x, 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*/