Where A is a universal differential operator, B a boundary operator, f(r) a known analytical function, (Γ) is the boundary of the domain (Ω) and (∂u/∂n) denotes differentiation along the normal engrossed outwards from (Ω). A can be segregated into two sectors which are L and N , where L is the linear sector andN is nonlinear sector. Eq. (18) can therefore be rewritten as follows: