Actual source code: ex9f.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. VecCreateGhost() 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 finclude/petsc.h
28: #include finclude/petscvec.h
30: PetscMPIInt rank,size
31: PetscInt nlocal,nghost,ifrom(2)
32: PetscInt ierr,i,rstart,rend,ione
33: PetscTruth flag
34: PetscScalar value,tarray(20)
35: Vec lx,gx,gxs
37: nlocal = 6
38: nghost = 2
40: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
41: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
42: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
44: if (size .ne. 2) then
45: SETERRQ(1,'Must run with two processors',ierr)
46: endif
48: !
49: ! Construct a two dimensional graph connecting nlocal degrees of
50: ! freedom per processor. From this we will generate the global
51: ! indices of needed ghost values
52: !
53: ! For simplicity we generate the entire graph on each processor:
54: ! in real application the graph would stored in parallel, but this
55: ! example is only to demonstrate the management of ghost padding
56: ! with VecCreateGhost().
57: !
58: ! In this example we consider the vector as representing
59: ! degrees of freedom in a one dimensional grid with periodic
60: ! boundary conditions.
61: !
62: ! ----Processor 1--------- ----Processor 2 --------
63: ! 0 1 2 3 4 5 6 7 8 9 10 11
64: ! |----|
65: ! |-------------------------------------------------|
66: !
69: if (rank .eq. 0) then
70: ifrom(1) = 11
71: ifrom(2) = 6
72: else
73: ifrom(1) = 0
74: ifrom(2) = 5
75: endif
77: ! Create the vector with two slots for ghost points. Note that both
78: ! the local vector (lx) and the global vector (gx) share the same
79: ! array for storing vector values.
81: call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-allocate', &
82: & flag,ierr)
83: if (flag) then
84: call VecCreateGhostWithArray(PETSC_COMM_WORLD,nlocal, &
85: & PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
86: else
87: call VecCreateGhost(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE, &
88: & nghost,ifrom,gxs,ierr)
89: endif
92: ! Test VecDuplicate
94: call VecDuplicate(gxs,gx,ierr)
95: call VecDestroy(gxs,ierr)
97: ! Access the local Form
99: call VecGhostGetLocalForm(gx,lx,ierr)
101: ! Set the values from 0 to 12 into the "global" vector
103: call VecGetOwnershipRange(gx,rstart,rend,ierr)
105: ione = 1
106: do 10, i=rstart,rend-1
107: value = i
108: call VecSetValues(gx,ione,i,value,INSERT_VALUES,ierr)
109: 10 continue
111: call VecAssemblyBegin(gx,ierr)
112: call VecAssemblyEnd(gx,ierr)
114: call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
115: call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
117: ! Print out each vector, including the ghost padding region.
119: call VecView(lx,PETSC_VIEWER_STDOUT_SELF,ierr)
121: call VecGhostRestoreLocalForm(gx,lx,ierr)
122: call VecDestroy(gx,ierr)
123: call PetscFinalize(ierr)
124: end
125: