Actual source code: ex42.c
1: static char help[] = "Scatters from a parallel vector to a parallel vector.\n\n";
3: #include <petscvec.h>
5: int main(int argc, char **argv)
6: {
7: PetscInt n = 5, N, i;
8: PetscMPIInt size, rank;
9: PetscScalar value, zero = 0.0;
10: Vec x, y;
11: IS is1, is2;
12: VecScatter ctx = 0;
14: PetscFunctionBeginUser;
15: PetscCall(PetscInitialize(&argc, &argv, (char *)0, help));
16: PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
17: PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
19: /* create two vectors */
20: N = size * n;
21: PetscCall(VecCreate(PETSC_COMM_WORLD, &y));
22: PetscCall(VecSetSizes(y, n, PETSC_DECIDE));
23: PetscCall(VecSetFromOptions(y));
25: PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
26: PetscCall(VecSetSizes(x, n, PETSC_DECIDE));
27: PetscCall(VecSetFromOptions(x));
29: /* create two index sets */
30: PetscCall(ISCreateStride(PETSC_COMM_WORLD, n, n * rank, 1, &is1));
31: PetscCall(ISCreateStride(PETSC_COMM_WORLD, n, (n * (rank + 1)) % N, 1, &is2));
33: /* fill local part of parallel vector x */
34: value = (PetscScalar)(rank + 1);
35: for (i = n * rank; i < n * (rank + 1); i++) PetscCall(VecSetValues(x, 1, &i, &value, INSERT_VALUES));
36: PetscCall(VecAssemblyBegin(x));
37: PetscCall(VecAssemblyEnd(x));
39: PetscCall(VecSet(y, zero));
41: PetscCall(VecScatterCreate(x, is1, y, is2, &ctx));
42: for (i = 0; i < 100; i++) {
43: PetscReal ynorm;
44: PetscInt j;
45: PetscCall(VecNormBegin(y, NORM_2, &ynorm));
46: PetscCall(PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)y)));
47: for (j = 0; j < 3; j++) {
48: PetscCall(VecScatterBegin(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
49: PetscCall(VecScatterEnd(ctx, x, y, ADD_VALUES, SCATTER_FORWARD));
50: }
51: PetscCall(VecNormEnd(y, NORM_2, &ynorm));
52: /* PetscCall(PetscPrintf(PETSC_COMM_WORLD,"ynorm = %8.2G\n",ynorm)); */
53: }
54: PetscCall(VecScatterDestroy(&ctx));
55: PetscCall(VecView(y, PETSC_VIEWER_STDOUT_WORLD));
57: PetscCall(VecDestroy(&x));
58: PetscCall(VecDestroy(&y));
59: PetscCall(ISDestroy(&is1));
60: PetscCall(ISDestroy(&is2));
62: PetscCall(PetscFinalize());
63: return 0;
64: }