anchor.diff:    subroutine PRMS(y,yrms,ierr)
       ! declarations
       implicit none
  +    include "mpif.h"
       integer, intent(out) :: ierr
       real*8,  intent(in)  :: y(nxl,nyl)
       real*8,  intent(out) :: yrms
  
positive.code:   subroutine Exchange(y, ierr)
      ! declarations
      implicit none
      real*8,  intent(in)  :: y(nxl,nyl)
      integer, intent(out) :: ierr
      integer :: reqSW, reqSE, reqSS, reqSN, reqRW, reqRE, reqRS, reqRN;
  
negative.code: ! Main driver program
  !-----------------------------------------------------------------
  program driver
  
    ! inclusions
    use UserData
    implicit none
    include "mpif.h"
  
    ! Declarations
    ! general problem parameters
    real*8,    parameter :: pi = 3.1415926535897932d0
    real*8,    parameter :: T0 = 0.d0     ! initial time 
  