anchor.diff:    if (.not. RedGrav) then
       ! Initialise arrays for pressure solver
       ! a = derivatives of the depth field
  -      call derivatives_of_the_depth_field(a, depth, g_vec(1), dx, dy, nx, ny)
  +      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
  
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:   end do
  
    return
  end subroutine calc_A_matrix
  
  ! ---------------------------------------------------------------------------
  
  