Actual source code: ex25.c
petsc-3.13.4 2020-08-01
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: {
10: PetscInt n = 5,N,low,high,iglobal,i;
11: PetscMPIInt size,rank;
12: PetscScalar value,zero = 0.0;
13: Vec x,y;
14: IS is1,is2;
15: VecScatter ctx;
17: PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;
18: MPI_Comm_size(PETSC_COMM_WORLD,&size);
19: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
21: /* create two vectors */
22: N = size*n;
23: VecCreate(PETSC_COMM_WORLD,&y);
24: VecSetSizes(y,PETSC_DECIDE,N);
25: VecSetFromOptions(y);
26: if (!rank) {
27: VecCreateSeq(PETSC_COMM_SELF,N,&x);
28: } else {
29: VecCreateSeq(PETSC_COMM_SELF,0,&x);
30: }
32: /* create two index sets */
33: if (!rank) {
34: ISCreateStride(PETSC_COMM_SELF,N,0,1,&is1);
35: ISCreateStride(PETSC_COMM_SELF,N,0,1,&is2);
36: } else {
37: ISCreateStride(PETSC_COMM_SELF,0,0,1,&is1);
38: ISCreateStride(PETSC_COMM_SELF,0,0,1,&is2);
39: }
41: VecSet(x,zero);
42: VecGetOwnershipRange(y,&low,&high);
43: for (i=0; i<n; i++) {
44: iglobal = i + low; value = (PetscScalar) (i + 10*rank);
45: VecSetValues(y,1,&iglobal,&value,INSERT_VALUES);
46: }
47: VecAssemblyBegin(y);
48: VecAssemblyEnd(y);
49: VecView(y,PETSC_VIEWER_STDOUT_WORLD);
51: VecScatterCreate(y,is2,x,is1,&ctx);
52: VecScatterBegin(ctx,y,x,ADD_VALUES,SCATTER_FORWARD);
53: VecScatterEnd(ctx,y,x,ADD_VALUES,SCATTER_FORWARD);
54: VecScatterDestroy(&ctx);
56: if (!rank) {
57: printf("----\n");
58: VecView(x,PETSC_VIEWER_STDOUT_SELF);
59: }
61: VecDestroy(&x);
62: VecDestroy(&y);
63: ISDestroy(&is1);
64: ISDestroy(&is2);
66: PetscFinalize();
67: return ierr;
68: }
72: /*TEST
74: test:
75: nsize: 3
77: TEST*/