1: !
  2: !     "$Id: ex14f.F,v 1.9 2001/08/07 03:02:34 balay Exp $";
  3: !
  4: ! Description: Illustrates the use of VecCreateGhost()
  5: !
  6: !/*T
  7: !   Concepts: vectors^assembling vectors;
  8: !   Concepts: vectors^ghost padding;
  9: !   Processors: n
 10: !
 11: !   Description: Ghost padding is one way to handle local calculations that
 12: !      involve values from other processors. VecCreateGhostBlock() provides
 13: !      a way to create vectors with extra room at the end of the vector 
 14: !      array to contain the needed ghost values from other processors, 
 15: !      vector computations are otherwise unaffected.
 16: !T*/

 18:       program main
 19:       implicit none

 21: !
 22: !  The following include statements are required for Fortran programs
 23: !  that use PETSc vectors:
 24: !     petsc.h       - base PETSc routines
 25: !     petscvec.h    - vectors
 26: !

 28:  #include include/finclude/petsc.h
 29:  #include include/finclude/petscvec.h

 31:       integer      rank,nlocal,nghost,ifrom(2),size,ierr,i,rstart,rend
 32:       integer      flag,bs
 33:       PetscScalar  value,tarray(20)
 34:       Vec          lx,gx,gxs

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

 41:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 42:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
 43:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)

 45:       if (size .ne. 2) then
 46:        SETERRQ(1,'Must run with two processors')
 47:       endif

 49: !
 50: !     Construct a two dimensional graph connecting nlocal degrees of
 51: !     freedom per processor. From this we will generate the global
 52: !     indices of needed ghost values
 53: !
 54: !     For simplicity we generate the entire graph on each processor:
 55: !     in real application the graph would stored in parallel, but this
 56: !     example is only to demonstrate the management of ghost padding
 57: !     with VecCreateGhost().
 58: !
 59: !     In this example we consider the vector as representing
 60: !     degrees of freedom in a one dimensional grid with periodic
 61: !     boundary conditions.
 62: !
 63: !        ----Processor  1-----------  ----Processor 2 --------
 64: !         0 1 2 3 4 5 6 7 8 9 10 11    12 13 14 15 16 17 18 19 20 21 22 23
 65: !                              |--|----|---|
 66: !         |-|--------------------------------------------------------|--|
 67: !


 70:       if (rank .eq. 0) then
 71:         ifrom(1) = bs*11
 72:         ifrom(2) = bs*6
 73:       else
 74:         ifrom(1) = bs*0
 75:         ifrom(2) = bs*5
 76:       endif

 78: !     Create the vector with two slots for ghost points. Note that both
 79: !     the local vector (lx) and the global vector (gx) share the same
 80: !     array for storing vector values.

 82:       call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-allocate',flag,ierr)
 83:       if (flag .ne. 0) then
 84:         call VecCreateGhostBlockWithArray(PETSC_COMM_WORLD,bs,nlocal,    &
 85:      &        PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
 86:       else
 87:         call VecCreateGhostBlock(PETSC_COMM_WORLD,bs,nlocal,             &
 88:      &       PETSC_DECIDE,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:        do 10, i=rstart,rend-1
106:          value = i
107:          call VecSetValues(gx,1,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: