Optimum accelerating factor for s.o.r. solutions of domains containing ∂ϕ∂n = 0 boundary conditions

The letter describes a simple and useful extension of existing theory on the determination of optimum accelerating factor for successive over-relaxation applied to solutions of Laplace´s and Poisson´s equations. In particular, domains where the condition ∂ϕ∂n = 0 is applied along part of the boundary contour are considered. The boundary along which this condition is applied need not be linear.