P-R Method for 2D heat equation on unit square %
% u_t = u_{xx} + u_{yy} + f(x,t) %
% Test problme: %
% Exact solution: u(t,x,y) = exp(-pi^2*t) sin(pi*x+pi*y) %
% Source term: f(t,x,y) = pi^2*exp(-pi^2*t) sin(pi*x+pi*y) %
% Files needed for the test: %
% adi.m: This file, the main calling code. %
% f.m: The file defines the f(t,x,y) %
% uexact.m: The exact solution.