Problems with PDE (pdepe)

*I'm trying to solve the following pde in MATLAB, with pdepe:

Equation: du/dt = d^2(x)/dx^2

Initial condition: u'(0) = 0

Boundary conditions: u(0) = 20, u(1) = 5

I have everything in place, except the initial condition, which only seems to accept constants or simple expressions. My question is therefore: how can i define the initial condition as u'(0) = 0?

Below, the IC is set to 10 in lack of anything better. The code is as follows:* %------------------------------------------------------------------

function pdex1

m = 0;

x = linspace(0,20,40);

t = linspace(0,20,40);

sol = pdepe(m,@pdex1pde,@pdex1ic,@pdex1bc,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 20 mesh points.')

xlabel('Distance x')

ylabel('Time t')

% A solution profile can also be illuminating.

figure

plot(x,u(end,:))

title('Solution at t = 10')

xlabel('Distance x')

ylabel('u(x,t)')

% --------------------------------------------------------------

function [c,f,s] = pdex1pde(x,t,u,DuDx)

c = 1;

f = 0.00001*DuDx;

s = 0.5;

% --------------------------------------------------------------

function u0 = pdex1ic(x) u0 = 10

% --------------------------------------------------------------

function [pl,ql,pr,qr] = pdex1bc(xl,ul,xr,ur,t)

pl = ul-20;

ql = 0;

pr = ur-5;

qr = 0;