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## Re: [ff3d-users] Strange error during execution

 From: Stephane Del Pino Subject: Re: [ff3d-users] Strange error during execution Date: Fri, 29 Dec 2006 01:50:48 +0100 User-agent: KMail/1.9.5

```Le jeudi 21 décembre 2006 09:15, Emilio Melero García a écrit :
> Dear Stephane,
Dear Emilio.

> thank you so much for your help and patience. I will certainly increase the
> time step. It is a very good solution even with the memory leak since i do
> not need to go foward in time so much (no more than 13 days, which are only
> 936 iterations with dt=1200).
>
> By the way, and i understand it is not the place to ask these, and that you
> might be very busy to answer, the stability condition that you mention and
> the residual of the conjugate gradient is due to the problem i am trying to
> solve or is inherent to the PDE solver you have implemented?, and if it is
> problem dependent, could you hint me on how did  you evaluate the residual
> and the stability?
First the residual:
- it is just written by ff3d when the default verbosity (3) is used.
- for your problem, it is always small because your time step so small that
the difference between u(n+1) and u(n) is very small...

Second concerning the stability:
The time scheme you use [u(n+1)-div(dt*grad(u(n+1))) = u(n)] is
unconditionally stable. This means that you can choose the time step
arbitrarily...

> And finally, i am trying to make my way into all this
> world of FEM problems and solvers, but i still have a notion that i might
> be resorted to implement my own very specific FEM code, any good book you
> would recommend to learn FEM methods and implementations?
Well there are many good books for finite elements. I recommend the book from
Ciarlet for the basis of the theoritical point of view. For the
implementation, there are a lot that depend on the physic you want to
simulate...

Anyway ff3d might be the solution to your problem: can you describe the
specificities you are facing?

Also, some people have already done it: you can modify ff3d to fit your needs
and if that can be useful for others you can then distribute your changes,

> Please, as i said i understand this might be not the place to ask these
> things but i have felt that  people in these list read the e-mails and
> answer when they can. So please, consider this a question to the people in
> the list.
No, I think it is a right place to ask this kind of question! Feel free for
that.

> Thank you very much from a newbie.
You are welcome!

Best regards,
Stephane.

PS: sorry for this late answer, due to holidays ;-)

```