anchor.diff:  
       end type
   
  -    contains 
  +    contains
   
       !
       ! Given an x, y point, and size=2 arrays periodic_xs, periodic_ys defining
  
positive.code:                 ! Neighbour domain index/image
                  n_ind = nint( all_recv_metadata(IND,i,j,ti))
                  n_img = nint( all_recv_metadata(IMG,i,j,ti))
                  n_row = nint( all_recv_metadata(7, i, j, ti)) 
                  n_comms = nint(all_send_metadata(8, n_row, n_ind, n_img) )
  
                  ! Check that boxes have the same x/y coordinates to within tolerable round-off
  
negative.code:                 ! Firstly, get centroid  coordinates, and determine if we are in the periodic region
                  ! These were constructed to never cross a periodic boundary
                  tmp_xs = domains(j)%x( domains(j)%nesting%recv_metadata(3:4,i) )
                  tmp_ys = domains(j)%y( domains(j)%nesting%recv_metadata(5:6,i) )
                  call check_periodic(tmp_xs(1), tmp_ys(1), periodic_xs, periodic_ys, in_periodic_region, &
                      adjust_coordinates=.FALSE.)
                  call check_periodic(tmp_xs(2), tmp_ys(2), periodic_xs, periodic_ys, in_periodic_region, &
  