This is our final numerical scheme for solving Laplace's equation. Poisson's equation adds only a minor complication to the above equation since in this case we have uxx+uyy=−ρ(x,y), and we need only to add a discretized version of ρ(x) resulting in ui,j=14[ui,j+1+ui,j−1+ui+1,j+ui−1,j]+h24ρi,j.