Actual source code: ex42.c
petsc-3.6.4 2016-04-12
2: static char help[] = "Scatters from a parallel vector to a parallel vector.\n\n";
4: #include <petscvec.h>
8: int main(int argc,char **argv)
9: {
11: PetscInt n = 5,N,i;
12: PetscMPIInt size,rank;
13: PetscScalar value,zero = 0.0;
14: Vec x,y;
15: IS is1,is2;
16: VecScatter ctx = 0;
18: PetscInitialize(&argc,&argv,(char*)0,help);
19: MPI_Comm_size(PETSC_COMM_WORLD,&size);
20: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
22: /* create two vectors */
23: N = size*n;
24: VecCreate(PETSC_COMM_WORLD,&y);
25: VecSetSizes(y,n,PETSC_DECIDE);
26: VecSetFromOptions(y);
28: VecCreate(PETSC_COMM_WORLD,&x);
29: VecSetSizes(x,n,PETSC_DECIDE);
30: VecSetFromOptions(x);
32: /* create two index sets */
33: ISCreateStride(PETSC_COMM_WORLD,n,n*rank,1,&is1);
34: ISCreateStride(PETSC_COMM_WORLD,n,(n*(rank+1))%N,1,&is2);
36: /* fill local part of parallel vector x */
37: value = (PetscScalar)(rank+1);
38: for (i=n*rank; i<n*(rank+1); i++) {
39: VecSetValues(x,1,&i,&value,INSERT_VALUES);
40: }
41: VecAssemblyBegin(x);
42: VecAssemblyEnd(x);
44: VecSet(y,zero);
46: VecScatterCreate(x,is1,y,is2,&ctx);
47: for (i=0; i<100; i++) {
48: PetscReal ynorm;
49: PetscInt j;
50: VecNormBegin(y,NORM_2,&ynorm);
51: PetscCommSplitReductionBegin(PetscObjectComm((PetscObject)y));
52: for (j=0; j<3; j++) {
53: VecScatterBegin(ctx,x,y,ADD_VALUES,SCATTER_FORWARD);
54: VecScatterEnd(ctx,x,y,ADD_VALUES,SCATTER_FORWARD);
55: }
56: VecNormEnd(y,NORM_2,&ynorm);
57: /* PetscPrintf(PETSC_COMM_WORLD,"ynorm = %8.2G\n",ynorm); */
58: }
59: VecScatterDestroy(&ctx);
60: VecView(y,PETSC_VIEWER_STDOUT_WORLD);
62: VecDestroy(&x);
63: VecDestroy(&y);
64: ISDestroy(&is1);
65: ISDestroy(&is2);
67: PetscFinalize();
68: return 0;
69: }