Actual source code: ex14f.F90
1: !
2: !
3: ! Description: Illustrates the use of VecCreateGhost()
4: !
5: !
6: ! Ghost padding is one way to handle local calculations that
7: ! involve values from other processors. VecCreateGhostBlock() provides
8: ! a way to create vectors with extra room at the end of the vector
9: ! array to contain the needed ghost values from other processors,
10: ! vector computations are otherwise unaffected.
11: !
13: program main
14: #include <petsc/finclude/petscvec.h>
15: use petscvec
16: implicit none
18: PetscMPIInt size, rank
19: PetscInt nlocal, nghost, ifrom(2)
20: PetscInt i, rstart, rend, bs, ione
21: PetscBool flag
22: PetscErrorCode ierr
23: PetscScalar value, tarray(20)
24: Vec lx, gx, gxs
25: PetscViewer singleton
27: nlocal = 6
28: nghost = 2
29: bs = 2
30: nlocal = bs*nlocal
32: PetscCallA(PetscInitialize(ierr))
33: PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD, rank, ierr))
34: PetscCallMPIA(MPI_Comm_size(PETSC_COMM_WORLD, size, ierr))
36: PetscCheckA(size == 2, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, 'Requires 2 processors')
38: !
39: ! Construct a two dimensional graph connecting nlocal degrees of
40: ! freedom per processor. From this we will generate the global
41: ! indices of needed ghost values
42: !
43: ! For simplicity we generate the entire graph on each processor:
44: ! in real application the graph would stored in parallel, but this
45: ! example is only to demonstrate the management of ghost padding
46: ! with VecCreateGhost().
47: !
48: ! In this example we consider the vector as representing
49: ! degrees of freedom in a one dimensional grid with periodic
50: ! boundary conditions.
51: !
52: ! ----Processor 1----------- ----Processor 2 --------
53: ! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
54: ! |--|----|---|
55: ! |-|--------------------------------------------------------|--|
56: !
58: if (rank == 0) then
59: ifrom(1) = 11
60: ifrom(2) = 6
61: else
62: ifrom(1) = 0
63: ifrom(2) = 5
64: end if
66: ! Create the vector with two slots for ghost points. Note that both
67: ! the local vector (lx) and the global vector (gx) share the same
68: ! array for storing vector values.
70: PetscCallA(PetscOptionsHasName(PETSC_NULL_OPTIONS, PETSC_NULL_CHARACTER, '-allocate', flag, ierr))
71: if (flag) then
72: PetscCallA(VecCreateGhostBlockWithArray(PETSC_COMM_WORLD, bs, nlocal, PETSC_DECIDE, nghost, ifrom, tarray, gxs, ierr))
73: else
74: PetscCallA(VecCreateGhostBlock(PETSC_COMM_WORLD, bs, nlocal, PETSC_DECIDE, nghost, ifrom, gxs, ierr))
75: end if
77: ! Test VecDuplicate
79: PetscCallA(VecDuplicate(gxs, gx, ierr))
80: PetscCallA(VecDestroy(gxs, ierr))
82: ! Access the local Form
84: PetscCallA(VecGhostGetLocalForm(gx, lx, ierr))
86: ! Set the values from 0 to 12 into the "global" vector
88: PetscCallA(VecGetOwnershipRange(gx, rstart, rend, ierr))
90: ione = 1
91: do 10, i = rstart, rend - 1
92: value = i
93: PetscCallA(VecSetValues(gx, ione, [i], [value], INSERT_VALUES, ierr))
94: 10 continue
96: PetscCallA(VecAssemblyBegin(gx, ierr))
97: PetscCallA(VecAssemblyEnd(gx, ierr))
99: PetscCallA(VecGhostUpdateBegin(gx, INSERT_VALUES, SCATTER_FORWARD, ierr))
100: PetscCallA(VecGhostUpdateEnd(gx, INSERT_VALUES, SCATTER_FORWARD, ierr))
102: ! Print out each vector, including the ghost padding region.
104: PetscCallA(PetscViewerGetSubViewer(PETSC_VIEWER_STDOUT_WORLD, PETSC_COMM_SELF, singleton, ierr))
105: PetscCallA(VecView(lx, singleton, ierr))
106: PetscCallA(PetscViewerRestoreSubViewer(PETSC_VIEWER_STDOUT_WORLD, PETSC_COMM_SELF, singleton, ierr))
108: PetscCallA(VecGhostRestoreLocalForm(gx, lx, ierr))
109: PetscCallA(VecDestroy(gx, ierr))
110: PetscCallA(PetscFinalize(ierr))
111: end
113: !/*TEST
114: !
115: ! test:
116: ! nsize: 2
117: !
118: !TEST*/