Numerical AnalysisPrograms Supporting AlgorithmsApplets by Richard Nunoo, book by Dr. Richard Burden and Dr. D. Faires. 

Poisson Equation FiniteDifference AlgorithmTo approximate the solution of the Poisson equation D(D(u)) = F(x,y), a<= x <= b, c <= y <= d, Subject to the boundary conditions: u(x,y) = G(x,y) if x = a or x = b for c <= y <= d, if y = c or y = d for a <= x <= b. 

