Actual source code: ex14f.F

  1: !
  2: !     "$Id: ex14f.F,v 1.8 2001/01/17 22:21:32 bsmith Exp $";
  3: !
  4: ! Description: Illustrates the use of VecCreateGhost()
  5: !
  6: !/*T
  7: !   Concepts: vectors^assembling vectors; ghost padding
  8: !   Processors: n
  9: !
 10: !   Comment: 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:       integer    rank,nlocal,nghost,ifrom(2),size,ierr,i,rstart,rend
 31:       integer    flag,bs
 32:       Scalar     value,tarray(20)
 33:       Vec        lx,gx,gxs

 35:       nlocal = 6
 36:       nghost = 2
 37:       bs     = 2
 38:       nlocal = bs*nlocal

 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')
 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    12 13 14 15 16 17 18 19 20 21 22 23
 64: !                              |--|----|---|
 65: !         |-|--------------------------------------------------------|--|
 66: !


 69:       if (rank .eq. 0) then
 70:         ifrom(1) = bs*11
 71:         ifrom(2) = bs*6
 72:       else
 73:         ifrom(1) = bs*0
 74:         ifrom(2) = bs*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',flag,ierr)
 82:       if (flag .ne. 0) then
 83:         call VecCreateGhostBlockWithArray(PETSC_COMM_WORLD,bs,nlocal,    &
 84:      &        PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
 85:       else
 86:         call VecCreateGhostBlock(PETSC_COMM_WORLD,bs,nlocal,             &
 87:      &       PETSC_DECIDE,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:        do 10, i=rstart,rend-1
105:          value = i
106:          call VecSetValues(gx,1,i,value,INSERT_VALUES,ierr)
107:  10    continue

109:        call VecAssemblyBegin(gx,ierr)
110:        call VecAssemblyEnd(gx,ierr)

112:        call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
113:        call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)

115: !     Print out each vector, including the ghost padding region.

117:        call VecView(lx,PETSC_VIEWER_STDOUT_SELF,ierr)

119:        call VecGhostRestoreLocalForm(gx,lx,ierr)
120:        call VecDestroy(gx,ierr)
121:        call PetscFinalize(ierr)
122:        end
123: