Actual source code: ex14f.F90

  1: !
  2: !
  3: ! Description: Illustrates the use of VecCreateGhost()
  4: !
  5: !
  6: !      Ghost padding is one way to handle local calculations that
  7: !      involve values from other processors. VecCreateGhostBlock() provides
  8: !      a way to create vectors with extra room at the end of the vector
  9: !      array to contain the needed ghost values from other processors,
 10: !      vector computations are otherwise unaffected.
 11: !

 13:       program main
 14: #include <petsc/finclude/petscvec.h>
 15:       use petscvec
 16:       implicit none

 18:       PetscMPIInt size,rank
 19:       PetscInt nlocal,nghost,ifrom(2)
 20:       PetscInt i,rstart,rend,bs,ione
 21:       PetscBool       flag
 22:       PetscErrorCode ierr
 23:       PetscScalar  value,tarray(20)
 24:       Vec          lx,gx,gxs
 25:       PetscViewer singleton

 27:       nlocal = 6
 28:       nghost = 2
 29:       bs     = 2
 30:       nlocal = bs*nlocal

 32:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 33:       if (ierr .ne. 0) then
 34:         print*,'Unable to initialize PETSc'
 35:         stop
 36:       endif
 37:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
 38:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)

 40:       if (size .ne. 2) then; SETERRA(PETSC_COMM_WORLD,PETSC_ERR_WRONG_MPI_SIZE,'Requires 2 processors'); endif

 42: !
 43: !     Construct a two dimensional graph connecting nlocal degrees of
 44: !     freedom per processor. From this we will generate the global
 45: !     indices of needed ghost values
 46: !
 47: !     For simplicity we generate the entire graph on each processor:
 48: !     in real application the graph would stored in parallel, but this
 49: !     example is only to demonstrate the management of ghost padding
 50: !     with VecCreateGhost().
 51: !
 52: !     In this example we consider the vector as representing
 53: !     degrees of freedom in a one dimensional grid with periodic
 54: !     boundary conditions.
 55: !
 56: !        ----Processor  1-----------  ----Processor 2 --------
 57: !         0 1 2 3 4 5 6 7 8 9 10 11    12 13 14 15 16 17 18 19 20 21 22 23
 58: !                              |--|----|---|
 59: !         |-|--------------------------------------------------------|--|
 60: !

 62:       if (rank .eq. 0) then
 63:         ifrom(1) = 11
 64:         ifrom(2) = 6
 65:       else
 66:         ifrom(1) = 0
 67:         ifrom(2) = 5
 68:       endif

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

 74:       call PetscOptionsHasName(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,   &
 75:      &                         '-allocate',flag,ierr)
 76:       if (flag) then
 77:         call VecCreateGhostBlockWithArray(PETSC_COMM_WORLD,bs,nlocal,    &
 78:      &        PETSC_DECIDE,nghost,ifrom,tarray,gxs,ierr)
 79:       else
 80:         call VecCreateGhostBlock(PETSC_COMM_WORLD,bs,nlocal,             &
 81:      &       PETSC_DECIDE,nghost,ifrom,gxs,ierr)
 82:       endif

 84: !      Test VecDuplicate

 86:       call VecDuplicate(gxs,gx,ierr)
 87:       call VecDestroy(gxs,ierr)

 89: !      Access the local Form

 91:       call VecGhostGetLocalForm(gx,lx,ierr)

 93: !     Set the values from 0 to 12 into the "global" vector

 95:       call VecGetOwnershipRange(gx,rstart,rend,ierr)

 97:       ione = 1
 98:       do 10, i=rstart,rend-1
 99:         value = i
100:         call VecSetValues(gx,ione,i,value,INSERT_VALUES,ierr)
101:  10   continue

103:       call VecAssemblyBegin(gx,ierr)
104:       call VecAssemblyEnd(gx,ierr)

106:       call VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)
107:       call VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD,ierr)

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

111:       call PetscViewerGetSubViewer(PETSC_VIEWER_STDOUT_WORLD,PETSC_COMM_SELF,singleton,ierr)
112:       call VecView(lx,singleton,ierr)
113:       call PetscViewerRestoreSubViewer(PETSC_VIEWER_STDOUT_WORLD,PETSC_COMM_SELF,singleton,ierr)

115:       call VecGhostRestoreLocalForm(gx,lx,ierr)
116:       call VecDestroy(gx,ierr)
117:       call PetscFinalize(ierr)
118:       end

120: !/*TEST
121: !
122: !     test:
123: !       nsize: 2
124: !
125: !TEST*/