anchor.diff:  
     ! ****************** serial reference version ******************
   
  +  ! start timer
  +  timespent = -omp_get_wtime();
  +
     ! main timeloop
     do it = 1, nt
   
  
positive.code: program extended_examples
  
    ! modules
  
    use constants, only: ir
  
  
negative.code:     call swap_data()
  
    end do
  
    ! stop timer
    timespent = timespent + omp_get_wtime();
    PRINT *, nt ' time steps took total ', timespent, ' seconds, average ', timespent/nt , ' seconds'
  
    ! ****************** cleanup ******************
  
  