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[ff3d-users] Re: Negative values, memory=none

From: Stephane Del Pino
Subject: [ff3d-users] Re: Negative values, memory=none
Date: Fri, 28 Nov 2003 19:52:21 +0100
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On Thursday 27 November 2003 10:19, Joerg R. Weimar wrote:
 > I have a few questions:
> 1. Does ff3d have a bug preventing it from using negative values?
> The attached problem "negtest.txt" should generate a linear solution
> ranging from -1 to 1, but somehow generates 1-0-1. This is not just in
> the output, but also in the data, as can be seen from the integral
> evaluation.

I have been fighting a terrible bug few weeks ago and I just forgot to remove 
some debugging code and this leads to some unstabilities...
Thanks to you I removed the an absolute value function call that I forgot. It 
should work properly by now...

> 2. When selecting option memory(matrix=none), one must also set
>       method(type=penalty)
> if dirichlet boundary conditions are present. This is not the default,
> contrary to the information in the docs. Is this correct?

You are right. Default method is *always* elimination. It is easier to use. 
With penalty you may have to choose the value of epsilon... The documentation 
is quite obsolete in some ways. I have to finish some implementation and then 
I will go back to the documentation ... Then I think ff3d will be ready for 
version 1.

> 3. Are any primitives beyond box,sphere,cylinder supported (or planned)?
>     I would like to see cone, surface of revolution, extrusion.
Yes. I tried to implement all the primitives from POV-Ray.
cone, torus and plane are already available.  If you need surface of 
revolution and extrusion quickly, I can try to provide them to you as soon as 
possible but only with linear interpolation in a first time. Please tell me.

> 4. I am trying to solve a combined problem in two domains:
> first solve on mesh M, then solve a similar problem on mesh M2, using
> the first solution as boundary condition. I cannot figure out how to do
> this correctly (See combined.txt).

I looked at you file. The method seems correct to me but it crashes since your 
second mesh M2 has a volume that is 0: b and c are both of the form (1,1,x). 
I should check that volume is not 0...
Does this answer to your question?

Best regards,
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