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: