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## Re: [Getfem-users] Transient analysis-dirichlet conditions

 From: Yves Renard Subject: Re: [Getfem-users] Transient analysis-dirichlet conditions Date: Wed, 4 Jun 2008 16:01:15 +0200 User-agent: KMail/1.9.5

```On Wednesday 04 June 2008 10:30, Sébastien Janas wrote:
> Hi all,
>
> I want to solve the transient linear equation of diffusion.
>
> It seems that there is no function pre-build in getfem for the
> transient problems. So I assemble the mass matrix (MM) and stiffness
> matrix (SM) "manually", and then construct the linear system A*X=B
> using the backward euler
>
> A = (MM + delta t * SM)
> B = MM * X(t-1)
>
> Then I have to impose dirichlet conditions on the surface. I import my
> mesh from gmsh, where the surface are tagged with a number (in my case
> 200). How can I modify my linear system to take into accompt the
> dirichlet conditions? All the functions I found in the documentation
> are in the case where you use model bricks or standard assembly
> procedures...
>
> If I can have the list of node numbers tagged by 200 I would use the
> penalty method. But I am not able to obtain these list.
>
> I am using the python interface of getfem.
>
>
> Best regards,
>
> Janas Sébastien

This is true that there is no general strategy proposed for transient
problems, especially with the matlab or python interfaces.  This is however
not easy to build such a general strategy since the situation can vary a lot
for differente time integration schemes.

However, You can have the list of nodes on a boundary with the command

gf_mesh_fem_get(MF, 'dof on region', [bnum]);

but you have first to tag the boundary with the command

gf_mesh_set(M, 'region', int bnum, imat CVFLST);

(see the Matlab examples).

Yves.

--

Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
Pole de Mathematiques, INSA de Lyon          fax : (33) 04.72.43.85.29
20, rue Albert Einstein
69621 Villeurbanne Cedex, FRANCE
http://math.univ-lyon1.fr/~renard

---------

```