anchor.diff:    !
     ! ------------------------- negative 2 time step --------------------------
     ! Code to work out dhdtveryold, dudtveryold and dvdtveryold
  -  if (myid .eq. 0) then
   
     call state_derivative(dhdtveryold, dudtveryold, dvdtveryold, &
         h, u, v, depth, &
  
positive.code:   call wrap_fields_3D(v, nx, ny, layers)
    call wrap_fields_3D(h, nx, ny, layers)
  
    end if
    ! Now the model is ready to start.
    ! - We have h, u, v at the zeroth time step, and the tendencies at
    !   two older time steps.
  
negative.code:     ! Apply the boundary conditions
      call apply_boundary_conditions(unew, hfacW, wetmask, nx, ny, layers)
      call apply_boundary_conditions(vnew, hfacS, wetmask, nx, ny, layers)
  
      ! Do the isopycnal layer physics
      if (.not. RedGrav) then
  