function heateqex2
% Solves a Dirichlet problem for the heat equation in a rod,
% this time with variable conductivity, 21 mesh points.
m = 0;  % This simply means geometry is linear.
x = linspace(-5, 5, 21);
t = linspace(0, 4, 81);
sol = pdepe(m, @pdex, @pdexic, @pdexbc, x, t);
% Extract the first solution component as u.
u = sol(:,:,1);
% A surface plot is often a good way to study a solution.
surf(x, t, u)
title('Numerical solution computed with 21 mesh points in x')
xlabel('x'), ylabel('t'), zlabel('u')
% ----------------------------------------------------------
function [c, f, s] = pdex(x, t, u, DuDx)
c = 1;
f = (1 + (x/5).^2)*DuDx;  % flux = conductivity times u_x
s = 0;
% ----------------------------------------------------------
function u0 = pdexic(x)
u0 = 20 + 5*sign(x);  % initial condition at t = 0
% ----------------------------------------------------------
function [pl, ql, pr, qr] = pdexbc(xl, ul, xr, ur, t)
% q's are zero since we have Dirichlet conditions
% pl = 0 at the left, pr = 0 at the right endpoint
pl = ul - 15;
ql = 0;
pr = ur - 25;
qr = 0;