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 include/finclude/petsc.h
28: #include include/finclude/petscvec.h
30: PetscMPIInt rank,size
31: PetscInt nlocal,nghost,ifrom(2),ierr,i,rstart,rend,ione
32: PetscTruth flag
33: PetscScalar value,tarray(20)
34: Vec lx,gx,gxs
36: nlocal = 6
37: nghost = 2
39: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
40: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
41: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
43: if (size .ne. 2) then
44: SETERRQ(1,'Must run with two processors',ierr)
45: endif
47: !
48: ! Construct a two dimensional graph connecting nlocal degrees of
49: ! freedom per processor. From this we will generate the global
50: ! indices of needed ghost values
51: !
52: ! For simplicity we generate the entire graph on each processor:
53: ! in real application the graph would stored in parallel, but this
54: ! example is only to demonstrate the management of ghost padding
55: ! with VecCreateGhost().
56: !
57: ! In this example we consider the vector as representing
58: ! degrees of freedom in a one dimensional grid with periodic
59: ! boundary conditions.
60: !
61: ! ----Processor 1--------- ----Processor 2 --------
62: ! 0 1 2 3 4 5 6 7 8 9 10 11
63: ! |----|
64: ! |-------------------------------------------------|
65: !
68: if (rank .eq. 0) then
69: ifrom(1) = 11
70: ifrom(2) = 6
71: else
72: ifrom(1) = 0
73: ifrom(2) = 5
74: endif
76: ! Create the vector with two slots for ghost points. Note that both
77: ! the local vector (lx) and the global vector (gx) share the same
78: ! array for storing vector values.
80: call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-allocate', &
81: & flag,ierr)
82: if (flag .ne. 0) then
83: call VecCreateGhostWithArray(PETSC_COMM_WORLD,nlocal, &
84: & PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
85: else
86: call VecCreateGhost(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE, &
87: & nghost,ifrom,gxs,ierr)
88: endif
91: ! Test VecDuplicate
93: call VecDuplicate(gxs,gx,ierr)
94: call VecDestroy(gxs,ierr)
96: ! Access the local Form
98: call VecGhostGetLocalForm(gx,lx,ierr)
100: ! Set the values from 0 to 12 into the "global" vector
102: call VecGetOwnershipRange(gx,rstart,rend,ierr)
104: ione = 1
105: do 10, i=rstart,rend-1
106: value = i
107: call VecSetValues(gx,ione,i,value,INSERT_VALUES,ierr)
108: 10 continue
110: call VecAssemblyBegin(gx,ierr)
111: call VecAssemblyEnd(gx,ierr)
113: call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
114: call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
116: ! Print out each vector, including the ghost padding region.
118: call VecView(lx,PETSC_VIEWER_STDOUT_SELF,ierr)
120: call VecGhostRestoreLocalForm(gx,lx,ierr)
121: call VecDestroy(gx,ierr)
122: call PetscFinalize(ierr)
123: end
124: