anchor.diff:    end do
   
     return
  -end subroutine derivatives_of_the_depth_field
  +end subroutine calc_A_matrix
   
   ! ---------------------------------------------------------------------------
   
  
positive.code: ! ---------------------------------------------------------------------------
  !> Compute derivatives of the depth field for the pressure solver
  
  subroutine derivatives_of_the_depth_field(a, depth, g, dx, dy, nx, ny)
    implicit none
  
    double precision, intent(out) :: a(5, nx, ny)
  
negative.code:   if (.not. RedGrav) then
      ! Initialise arrays for pressure solver
      ! a = derivatives of the depth field
        call calc_A_matrix(a, depth, g_vec(1), dx, dy, nx, ny)
  
  #ifndef useExtSolver
      ! Calculate the spectral radius of the grid for use by the
  