Why this code does not run?

Hi, I am trying to learn how to solve PDEs. Here is the example from MatLab itself. But it did not run. I dont know what is missing . Anyone can help? thanks Ming

[Edit SCd: code formatting]

function [c,f,s] = pdex1pde(x,t,u,DuDx)
c = pi^2;
f = DuDx;
s = 0;

function u0 = pdex1ic(x)
u0 = sin(pi*x);

function [pl,ql,pr,qr] = pdex1bc(xl,ul,xr,ur,t)
pl = ul;
ql = 0;
pr = pi * exp(-t);
qr = 1;
x = linspace(0,1,20);
t = linspace(0,2,5);
m = 0;
sol = pdepe(m,@pdex1pde,@pdex1ic,@pdex1bc,x,t);
u = sol(:,:,1);
surf(x,t,u)

[Jan]

"It did not run" dows not contain enough information to understand the cause of the problem. Do you get an error message? How do you cal the function?

[sunnoom]

thank for comment. The error message was:

Input argument "DuDx" is undefined.

Error in ==> pdex1pde at 3

f = DuDx;

Thanks

[Walter Roberson]

That does sound odd.

I would put a breakpoint in that routine at the first line, and would check to see what parameters did get passed and their sizes.

Answer 1

[Jan]

"function [c,f,s] = pdex1pde(x,t,u,DuDx)" means, that you have to call the function pdex1pde with 4 input arguments. Did you call it manually without inputs?

Answer 2

[Wayne King]

Hi, Just enter

>>  pdex1

at the command prompt, that will run the demo.

[sunnoom]

yes, that can run the demo, but I want to know the code.

Answer 3

[Walter Roberson]

Where you have written

function [pl,ql,pr,qr] = pdex1bc(xl,ul,xr,ur,t)
pl = ul;
ql = 0;
pr = pi * exp(-t);
qr = 1;
x = linspace(0,1,20);
t = linspace(0,2,5);
m = 0;
sol = pdepe(m,@pdex1pde,@pdex1ic,@pdex1bc,x,t);
u = sol(:,:,1);
surf(x,t,u)

You need to break this up in to two parts:

function [pl,ql,pr,qr] = pdex1bc(xl,ul,xr,ur,t)
pl = ul;
ql = 0;
pr = pi * exp(-t);
qr = 1;

function sol = runpde
x = linspace(0,1,20);
t = linspace(0,2,5);
m = 0;
sol = pdepe(m,@pdex1pde,@pdex1ic,@pdex1bc,x,t);
u = sol(:,:,1);
surf(x,t,u)

and that new function needs to go first in the file if you are putting all of the routines in the same file.