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MathGroup Archive 2002

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  • To: mathgroup at
  • Subject: [mg35328] RE: [mg35297] Re: PDE
  • From: "DrBob" <majort at>
  • Date: Mon, 8 Jul 2002 03:19:56 -0400 (EDT)
  • Reply-to: <drbob at>
  • Sender: owner-wri-mathgroup at

The sign of your eigenvalues is wrong:

f = Sin[k x]*Sin[m y];
D[f, x, x] + D[f, y, y] // Factor

(-(k^2 + m^2))*Sin[k*x]*Sin[m*y]


-----Original Message-----
From: Jens-Peer Kuska [mailto:kuska at] 
To: mathgroup at
Subject: [mg35328] [mg35297] Re: PDE


no but ist is easy by hand -- use the eigenfunctions

Sin[k Pi x/L]*Sin[m Pi y/L] 

and the eigenvalues 

k^2 Pi^2/L^2 + m^2 Pi^2/L^2

and use the Fourier series. That's the simplest example
in standard text books about PDE's. You don't need a 
computer algebra
for that.


mitja Lakner wrote:
> Is there any package for solving eigenvalue problem for the Laplacian
> on the 2D (not rectangular) region with zero boundary value?
> f_{xx}+f_{yy}= t f
> Mitja Lakner

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