just use different color specification when calling plot : X = [-1:0.5:1]; % with black color x = [-1:0.2:1]; % with red color Y= ... ... <看更多>

First of all, your finite difference is wrong, as Steve pointed out. It has to be 1h2(−ui−1+2ui−ui+1)=1. This applies only to a structured grid (with ... ... <看更多>