Actual source code: ex2f.F

  1: !
  2: !    Description: Creates an index set based on a stride. Views that index set
  3: !    and then destroys it.
  4: !
  5: !/*T
  6: !    Concepts: index sets^manipulating a stride index set;
  7: !    Concepts: index sets^accessing indices from Fortran
  8: !T*/
  9: !
 10: !  Include petscis.h so we can use PETSc IS objects.
 11: !
 12:       program main
 13:       implicit none
 14:  #include finclude/petsc.h
 15:  #include finclude/petscis.h

 17:       PetscErrorCode ierr
 18:       PetscInt    i,n,index(1),first,step,val
 19:       IS          set
 20:       PetscOffset iss

 22: #define indices(ib)  index(iss + (ib))

 24:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 25:       n     = 10
 26:       first = 3
 27:       step  = 2

 29: !  Create stride index set, starting at 3 with a stride of 2
 30: !    Note each processor is generating its own index set
 31: !    (in this case they are all identical)

 33:       call ISCreateStride(PETSC_COMM_SELF,n,first,step,set,ierr)
 34:       call ISView(set,PETSC_VIEWER_STDOUT_SELF,ierr)

 36: !  Extract the indice values from the set. Demonstrates how a Fortran code can
 37: !  directly access the array storing a PETSc index set with ISGetIndices().
 38: !  The user declares an array (index(1)) and index variable (iss), which are
 39: !  then used together to allow the Fortran to directly manipulate the PETSc array

 41:       call ISGetIndices(set,index,iss,ierr)
 42:       write(6,20)
 43:       do 10 i=1,n
 44: !  Bug in IRIX64 f90 compiler - write cannot handle integer(integer*8) correctly
 45:          val = indices(i)
 46:          write(6,30) val
 47:  10   continue
 48:  20   format('Printing indices directly')
 49:  30   format(i3)
 50:       call ISRestoreIndices(set,index,iss,ierr)

 52: !  Determine information on stride

 54:       call ISStrideGetInfo(set,first,step,ierr)
 55:       if (first .ne. 3 .or. step .ne. 2) then
 56:         print*,'Stride info not correct!'
 57:       endif

 59:       call ISDestroy(set,ierr)
 60:       call PetscFinalize(ierr)
 61:       end