Actual source code: ex25.c
2: static char help[] = "Scatters from a parallel vector to a sequential vector. In\n\
3: this case processor zero is as long as the entire parallel vector; rest are zero length.\n\n";
5: #include <petscvec.h>
7: int main(int argc, char **argv)
8: {
9: PetscInt n = 5, N, low, high, iglobal, i;
10: PetscMPIInt size, rank;
11: PetscScalar value, zero = 0.0;
12: Vec x, y;
13: IS is1, is2;
14: VecScatter ctx;
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: N = size * n;
23: PetscCall(VecCreate(PETSC_COMM_WORLD, &y));
24: PetscCall(VecSetSizes(y, PETSC_DECIDE, N));
25: PetscCall(VecSetFromOptions(y));
26: if (rank == 0) {
27: PetscCall(VecCreateSeq(PETSC_COMM_SELF, N, &x));
28: } else {
29: PetscCall(VecCreateSeq(PETSC_COMM_SELF, 0, &x));
30: }
32: /* create two index sets */
33: if (rank == 0) {
34: PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is1));
35: PetscCall(ISCreateStride(PETSC_COMM_SELF, N, 0, 1, &is2));
36: } else {
37: PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 1, &is1));
38: PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 1, &is2));
39: }
41: PetscCall(VecSet(x, zero));
42: PetscCall(VecGetOwnershipRange(y, &low, &high));
43: for (i = 0; i < n; i++) {
44: iglobal = i + low;
45: value = (PetscScalar)(i + 10 * rank);
46: PetscCall(VecSetValues(y, 1, &iglobal, &value, INSERT_VALUES));
47: }
48: PetscCall(VecAssemblyBegin(y));
49: PetscCall(VecAssemblyEnd(y));
50: PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));
52: PetscCall(VecScatterCreate(y, is2, x, is1, &ctx));
53: PetscCall(VecScatterBegin(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
54: PetscCall(VecScatterEnd(ctx, y, x, ADD_VALUES, SCATTER_FORWARD));
55: PetscCall(VecScatterDestroy(&ctx));
57: if (rank == 0) {
58: PetscCall(PetscPrintf(PETSC_COMM_SELF, "----\n"));
59: PetscCall(VecView(x, PETSC_VIEWER_STDOUT_SELF));
60: }
62: PetscCall(VecDestroy(&x));
63: PetscCall(VecDestroy(&y));
64: PetscCall(ISDestroy(&is1));
65: PetscCall(ISDestroy(&is2));
67: PetscCall(PetscFinalize());
68: return 0;
69: }
71: /*TEST
73: test:
74: nsize: 3
76: TEST*/