Actual source code: ex14f.F
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: ! petsc.h - base PETSc routines
24: ! petscvec.h - vectors
25: !
27: #include include/finclude/petsc.h
28: #include include/finclude/petscvec.h
30: PetscMPIInt size,rank
31: PetscInt nlocal,nghost,ifrom(2),i,rstart,rend,bs,ione
32: PetscTruth flag
33: PetscErrorCode ierr
34: PetscScalar value,tarray(20)
35: Vec lx,gx,gxs
37: nlocal = 6
38: nghost = 2
39: bs = 2
40: nlocal = bs*nlocal
42: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
43: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
44: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
46: if (size .ne. 2) then
47: SETERRQ(1,'Must run with two processors',ierr)
48: endif
50: !
51: ! Construct a two dimensional graph connecting nlocal degrees of
52: ! freedom per processor. From this we will generate the global
53: ! indices of needed ghost values
54: !
55: ! For simplicity we generate the entire graph on each processor:
56: ! in real application the graph would stored in parallel, but this
57: ! example is only to demonstrate the management of ghost padding
58: ! with VecCreateGhost().
59: !
60: ! In this example we consider the vector as representing
61: ! degrees of freedom in a one dimensional grid with periodic
62: ! boundary conditions.
63: !
64: ! ----Processor 1----------- ----Processor 2 --------
65: ! 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
66: ! |--|----|---|
67: ! |-|--------------------------------------------------------|--|
68: !
71: if (rank .eq. 0) then
72: ifrom(1) = bs*11
73: ifrom(2) = bs*6
74: else
75: ifrom(1) = bs*0
76: ifrom(2) = bs*5
77: endif
79: ! Create the vector with two slots for ghost points. Note that both
80: ! the local vector (lx) and the global vector (gx) share the same
81: ! array for storing vector values.
83: call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-allocate',flag, &
84: & ierr)
85: if (flag .ne. 0) then
86: call VecCreateGhostBlockWithArray(PETSC_COMM_WORLD,bs,nlocal, &
87: & PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
88: else
89: call VecCreateGhostBlock(PETSC_COMM_WORLD,bs,nlocal, &
90: & PETSC_DECIDE,nghost,ifrom,gxs,ierr)
91: endif
94: ! Test VecDuplicate
96: call VecDuplicate(gxs,gx,ierr)
97: call VecDestroy(gxs,ierr)
99: ! Access the local Form
101: call VecGhostGetLocalForm(gx,lx,ierr)
103: ! Set the values from 0 to 12 into the "global" vector
105: call VecGetOwnershipRange(gx,rstart,rend,ierr)
107: ione = 1
108: do 10, i=rstart,rend-1
109: value = i
110: call VecSetValues(gx,ione,i,value,INSERT_VALUES,ierr)
111: 10 continue
113: call VecAssemblyBegin(gx,ierr)
114: call VecAssemblyEnd(gx,ierr)
116: call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
117: call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
119: ! Print out each vector, including the ghost padding region.
121: call VecView(lx,PETSC_VIEWER_STDOUT_SELF,ierr)
123: call VecGhostRestoreLocalForm(gx,lx,ierr)
124: call VecDestroy(gx,ierr)
125: call PetscFinalize(ierr)
126: end
127: