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From: Xinbo on 25 Apr 2010 02:50
Hello everyone, this will be my first time posting, so please tell me if I do something wrong. Also this is quite urgent since I will be tested on this in 24 hours.

I am a second year university student, and I'm taking a computational methods course that uses matlab. I am a bit confused about the PDEtools program, namely how to set the coefficients for elliptic functions.
For example, if I have laplace's function of heat conduction
Uxx = Uyy
where Uxx is the second derivative of u with respect to x
Uyy is the second derivative of u with respect to y
how would I set the constants, c, a, and f?

Also, what if I have a more complicated problem such as
Uxx + Uyy + g(x,y) *U = f(x,y),
how should I set the coefficients for that?

Again this is a bit urgent, and thanks if anyone could help me out.
From: Bruno Luong on 25 Apr 2010 06:58
"Xinbo " <chengxinbo(a)hotmail.com> wrote in message <hr0oni$hk0$1(a)fred.mathworks.com>...
>
> For example, if I have laplace's function of heat conduction
> Uxx = Uyy
> where Uxx is the second derivative of u with respect to x
> Uyy is the second derivative of u with respect to y

The above is surely not elliptic/lapace/heat equation, it's wave/hyperbolic/helmoltz equation. I'm little concerned that you cannot discriminate among different kinds of PDE, let alone set it up and solve it (and in urgent).

Bruno
From: Xinbo on 25 Apr 2010 10:57

> The above is surely not elliptic/lapace/heat equation, it's wave/hyperbolic/helmoltz equation. I'm little concerned that you cannot discriminate among different kinds of PDE, let alone set it up and solve it (and in urgent).
>
> Bruno

Thank you Bruno for replying to this message. After posting this last night, I did some research online and eventually found a pdf file that distinguishes the different kinds of PDE for me. I am only required to know the elliptic PDEs, which are in the form of
Uxx + Uyy + g(x,y) U = f(x,y).
As for the laplace equation, I have only brought it up because it is the only kind of PDE I have solved in my differential equation course.

However, is there a way to export the graphical data obtained in PDE tools to numerical data? For example, if I would like to know the exactly value of U at (0,.5), how would I find that? Thanks.
From: Xinbo on 25 Apr 2010 11:07
Actually I have figured out how to find the value of U at a specific point, would there be a way to export the data as a x,y,U matrix? Thanks.
From: Steven Lord on 25 Apr 2010 23:32

"Xinbo " <chengxinbo(a)hotmail.com> wrote in message
news:hr1lqo$87s$1(a)fred.mathworks.com...
> Actually I have figured out how to find the value of U at a specific
> point, would there be a way to export the data as a x,y,U matrix? Thanks.

If you're referring to the PDETOOL GUI in Partial Differential Equations
Toolbox when you use the word "PDEtools", then look at the documentation.

http://www.mathworks.com/access/helpdesk/help/toolbox/pde/ug/bqivs1h-1.html

"Solve menu. From the Solve menu you solve the PDE. You can also open a
dialog box where you can adjust the solve parameters, and you can export the
solution to the workspace."

Also take a look at step 8 in the suggested modeling procedure:

http://www.mathworks.com/access/helpdesk/help/toolbox/pde/ug/bqivs1h-1.html#bqivs1h-13

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ


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