Actual source code: ex17f.F
1: !
2: !
3: ! "Scatters from a parallel vector to a sequential vector. In
4: ! this case each local vector is as long as the entire parallel vector.
5: !
6: implicit none
7: #include "finclude/petscsys.h"
8: #include "finclude/petscis.h"
9: #include "finclude/petscvec.h"
11: PetscErrorCode ierr
12: PetscMPIInt size,rank
13: PetscInt n,NN,low,high
14: PetscInt iglobal,i,ione
15: PetscInt first,stride
16: PetscScalar value,zero
17: Vec x,y
18: IS is1,is2
19: VecScatter ctx
21: n = 5
22: zero = 0.d0
23: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
25: call MPI_Comm_size(MPI_COMM_WORLD,size,ierr)
26: call MPI_Comm_rank(MPI_COMM_WORLD,rank,ierr)
28: ! create two vectors
29: ! one parallel and one sequential. The sequential one on each processor
30: ! is as long as the entire parallel one.
32: NN = size*n
34: call VecCreateMPI(MPI_COMM_WORLD,PETSC_DECIDE,NN,y,ierr)
35: call VecCreateSeq(MPI_COMM_SELF,NN,x,ierr)
37: call VecSet(x,zero,ierr)
38: call VecGetOwnershipRange(y,low,high,ierr)
39: ione = 1
40: do 10, i=0,n-1
41: iglobal = i + low
42: value = i + 10*rank
43: call VecSetValues(y,ione,iglobal,value,INSERT_VALUES,ierr)
44: 10 continue
46: call VecAssemblyBegin(y,ierr)
47: call VecAssemblyEnd(y,ierr)
48: !
49: ! View the parallel vector
50: !
51: call VecView(y,PETSC_VIEWER_STDOUT_WORLD,ierr)
53: ! create two index sets and the scatter context to move the contents of
54: ! of the parallel vector to each sequential vector. If you want the
55: ! parallel vector delivered to only one processor then create a is2
56: ! of length zero on all processors except the one to receive the parallel vector
58: first = 0
59: stride = 1
60: call ISCreateStride(PETSC_COMM_SELF,NN,first,stride,is1,ierr)
61: call ISCreateStride(PETSC_COMM_SELF,NN,first,stride,is2,ierr)
62: call VecScatterCreate(y,is2,x,is1,ctx,ierr)
63: call VecScatterBegin(ctx,y,x,ADD_VALUES,SCATTER_FORWARD,ierr)
64: call VecScatterEnd(ctx,y,x,ADD_VALUES,SCATTER_FORWARD,ierr)
65: call VecScatterDestroy(ctx,ierr)
66: !
67: ! View the sequential vector on the 0th processor
68: !
69: if (rank .eq. 0) then
70: call VecView(x,PETSC_VIEWER_STDOUT_SELF,ierr)
71: endif
73: call VecDestroy(x,ierr)
74: call VecDestroy(y,ierr)
75: call ISDestroy(is1,ierr)
76: call ISDestroy(is2,ierr)
78: call PetscFinalize(ierr)
79: end
80: