Actual source code: ex14f.F
petsc-3.5.4 2015-05-23
1: !
2: !
3: ! Description: Illustrates the use of VecCreateGhost()
4: !
5: !/*T
6: ! Concepts: vectors^assembling vectors;
7: ! Concepts: vectors^ghost padding;
8: ! Processors: n
9: !
10: ! Description: Ghost padding is one way to handle local calculations that
11: ! involve values from other processors. VecCreateGhostBlock() provides
12: ! a way to create vectors with extra room at the end of the vector
13: ! array to contain the needed ghost values from other processors,
14: ! vector computations are otherwise unaffected.
15: !T*/
17: program main
18: implicit none
20: !
21: ! The following include statements are required for Fortran programs
22: ! that use PETSc vectors:
23: ! petscsys.h - base PETSc routines
24: ! petscvec.h - vectors
25: !
27: #include <finclude/petscsys.h>
28: #include <finclude/petscvec.h>
30: PetscMPIInt size,rank
31: PetscInt nlocal,nghost,ifrom(2)
32: PetscInt i,rstart,rend,bs,ione
33: PetscBool flag
34: PetscErrorCode ierr
35: PetscScalar value,tarray(20)
36: Vec lx,gx,gxs
38: nlocal = 6
39: nghost = 2
40: bs = 2
41: nlocal = bs*nlocal
43: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
44: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
45: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
47: if (size .ne. 2) then
48: SETERRQ(PETSC_COMM_SELF,1,'Must run with two processors',ierr)
49: endif
51: !
52: ! Construct a two dimensional graph connecting nlocal degrees of
53: ! freedom per processor. From this we will generate the global
54: ! indices of needed ghost values
55: !
56: ! For simplicity we generate the entire graph on each processor:
57: ! in real application the graph would stored in parallel, but this
58: ! example is only to demonstrate the management of ghost padding
59: ! with VecCreateGhost().
60: !
61: ! In this example we consider the vector as representing
62: ! degrees of freedom in a one dimensional grid with periodic
63: ! boundary conditions.
64: !
65: ! ----Processor 1----------- ----Processor 2 --------
66: ! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
67: ! |--|----|---|
68: ! |-|--------------------------------------------------------|--|
69: !
72: if (rank .eq. 0) then
73: ifrom(1) = 11
74: ifrom(2) = 6
75: else
76: ifrom(1) = 0
77: ifrom(2) = 5
78: endif
80: ! Create the vector with two slots for ghost points. Note that both
81: ! the local vector (lx) and the global vector (gx) share the same
82: ! array for storing vector values.
84: call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-allocate',flag, &
85: & ierr)
86: if (flag) then
87: call VecCreateGhostBlockWithArray(PETSC_COMM_WORLD,bs,nlocal, &
88: & PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
89: else
90: call VecCreateGhostBlock(PETSC_COMM_WORLD,bs,nlocal, &
91: & PETSC_DECIDE,nghost,ifrom,gxs,ierr)
92: endif
95: ! Test VecDuplicate
97: call VecDuplicate(gxs,gx,ierr)
98: call VecDestroy(gxs,ierr)
100: ! Access the local Form
102: call VecGhostGetLocalForm(gx,lx,ierr)
104: ! Set the values from 0 to 12 into the "global" vector
106: call VecGetOwnershipRange(gx,rstart,rend,ierr)
108: ione = 1
109: do 10, i=rstart,rend-1
110: value = i
111: call VecSetValues(gx,ione,i,value,INSERT_VALUES,ierr)
112: 10 continue
114: call VecAssemblyBegin(gx,ierr)
115: call VecAssemblyEnd(gx,ierr)
117: call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
118: call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
120: ! Print out each vector, including the ghost padding region.
122: call VecView(lx,PETSC_VIEWER_STDOUT_SELF,ierr)
124: call VecGhostRestoreLocalForm(gx,lx,ierr)
125: call VecDestroy(gx,ierr)
126: call PetscFinalize(ierr)
127: end