Re: [Getfem-users] Example of a simple mixed-problem, or problem with two variables

[Renard Yves]

Dear Jehanzeb,

You have to use a volumic assembly . An example  for the matrix of the  
Laplace operator is

gf_asm('volumic',['a=data(#2); ',...
        
'M(#1,#1)+=sym(comp(Grad(#1).Grad(#1).Base(#2))(:,i,:,i,j).a(j))'],  
mim, mf, mf_data, A);

A matrix for a mixed term can be obtained in a same way with two mf :

 gf_asm('volumic', 'M(#1,#1)+=comp(Grad(#1).Base(#2))(:,i,i,:)', mim,  
mf1, mf2);

where mf1 should be a vectorial fem (for more details see the Getfem++  
documentation).

Yves.


Jehanzeb Hameed <address@hidden> a écrit :

> I had a look at the Stokes example. It uses model bricks to form the
> system. From the documentation, it seems using model bricks implicitly
> chooses the bilinear variational form. I would like to define my own
> bilinear form to form the matrix, in which I can define terms like
> div(q) + c u  (q = vector, c = constant, u = another variable besides
> q). How would I go about this?
>
> Thanks,
> -Jehanzeb
>
> On Sun, Jul 5, 2009 at 11:05 AM, Iago  
> Barbeiro<address@hidden> wrote:
> > Dear Jehanzeb,
> >
> > I think you may start by looking the Stokes example.
> > It deals with two variables (û=uî+v^j and p) and has the term div(û).dp.
> > Bon courage!
> >
> > Iago
> >
> > On Sun, Jul 5, 2009 at 6:07 AM, Jehanzeb Hameed <address@hidden>
> > wrote:
> > > Hello,
> > >
> > > Is there a simple example in getfem where assembly is for two
> > > variables? E.g. we may want to solve for "u" and "q" (with an equation
> > > defining the relationship between u and q) . Such a case arises in
> > > mixed methods.  Is there an example for mixed-poisson problem
> > > somewhere? I know mixed-elasticity problem is given with getfem, but I
> > > am not familiar with that particular problem.
> > >
> > > In particular, I am not sure how to refer to "q" and "u" in
> > > generic_assembly routines. Say my weak form involves div(q) . v ? How
> > > will I write this in "assem.set" routine? (I am guessing thats what I
> > > am supposed to do).
> > >
> > > Thanks,
> > > -Jehanzeb
> > >
> > > _______________________________________________
> > > Getfem-users mailing list
> > > address@hidden
> > > https://mail.gna.org/listinfo/getfem-users
>
> _______________________________________________
> Getfem-users mailing list
> address@hidden
> https://mail.gna.org/listinfo/getfem-users