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Re: [ff3d-users] Problem in Solving Laplace with Neumann BC's


From: Stephane Del Pino
Subject: Re: [ff3d-users] Problem in Solving Laplace with Neumann BC's
Date: Thu, 29 Apr 2010 08:32:03 +0200
User-agent: KMail/1.12.4 (Linux/2.6.32-3-amd64; KDE/4.3.4; x86_64; ; )

Hello.

Default setting for ff3d to solve linear systems is Conjugate Gradient with and 
epsilon of convergence set to 1E-5.

Here, to get a better solution, you need to get a smaller epsilon. Taking 1E-8 
seems enough for your case:

Use the conjugate gradient option in your solver block:

...
solve(v) in O by M
  cg(epsilon=1E-8)
{
...

Beware that your are solving your problem in a box which corresponds exactly 
to your fictitious domain geometry. This can eventually lead to strange 
behaviors. If your mesh fits the geometry I recommend not to use the fictitious 
domain but directly the conformal FEM. It is very simple in your case, write
...
solve(v) in M
  cg(epsilon=1E-8)
{
...

Best regards,
St├ęphane.






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