PDE with pdepe

Dear Forum,

I have two partial differential equations that describe heat conduction. I want to solve it with pdepe, just like in the example given in Matlab Help under System of PDEs. The Equations are:

1. DTp/Dt = ALPHAp* DTp/Dx + BETA*(Tm-Tp)
2. DTm/Dt = -ALPHAm*DTm/Dx - BETA* (Tm-Tp)

My Code is:

function [c,f,s]= unserepde ( x,t,u,DuDx)
c=[1;1];
%f = [0.024; 0.17] .* DuDx;
f=[10;0.15].*DuDx;
y=u(1)-u(2);
%F = exp(5.73*y)-exp(-11.47*y);
F=0.15*y;
s=[F;-F];
end

Initial Conditions:
function u0 = unsereic(x)
u0 = [20; 120];  

Boundary Conditions:
function [pl,ql,pr,qr] = unserebc(xl,ul,xr,ur,t)
pl = [-20*10; ul(2)-120];                              
ql = [1; 0];                                  
pr = [ur(1)-20; -120*0.15];                            
qr = [0; 1];

Plotting and solving would be:

x = [0 0.005 0.01 0.05 0.1 0.2 0.5 0.7 0.9 0.95 0.99 0.995 1];
t = [0 0.01 0.1 0.5 1 1.5 2 5 10 15 20 50 100 150];
m = 0;
sol = pdepe(m,@unserepde,@unsereic,@unserebc,x,t);
u1 = sol(:,:,1);
u2 = sol(:,:,2);
figure
surf(x,t,u1)
title('u1(x,t)')
xlabel('Distance x')
ylabel('Time t')
figure
surf(x,t,u2)
title('u2(x,t)')
xlabel('Distance x')
ylabel('Time t')

The Problem: the behaviour of the results doesn't make any sense. I have to use a negative alpha on 2. but Matlab doesn't allow to do so. I think I translated the two equations wrong into the Matlab Solver form. Could anybody help?

Thanks for your help, Yours sincerely, Markus

Answer 1

[Markus]

Can no one help?

Bye, Markus