Re: [Getfem-users] Problem assembling convection contribution

[Yves Renard]

On mercredi 10 février 2010, Cédric Venet wrote:
> Le 09/02/2010 22:44, Cédric Venet a écrit :
> > Le 09/02/2010 17:37, Yves Renard a écrit :
> >> On lundi 8 février 2010, Cédric Venet wrote:
> >>> Hi,
> >>>
> >>> I am trying to assemble the term "v.Grad u" where v is a field of
> >>> vector data on my mesh. u is a scalar field, and the unknow of my
> >>> equation. I am trying to do this:
> >>
> >> It is possible to have vector data, but you declaration seems to be
> >> wrong. It
> >> should be something like that :
> >>
> >> assem.set("F=data(1); G=data$2(qdim(#1), #1); M$1
> >> (#1,#1)+=comp(Base(#1).Grad(#1).Base(#1))(i,:,k,:).G(k,i).F(p)");
> >> assem.assembly();
> >>
> >> Yves.
> >
> > Hi,
> >
> > While this solve the parse problem, the answer is more complex and still
> > elude me.
> > My fem_mesh #1 has a qdim of 1, so with this solution, I hit the assert
> > invalid size for data argument. (my data vector is 3 times the number of
> > dof in #1). So my understanding is that I need a new fem_mesh #2, with a
> > qdim of 3. However, I didn't find a way to do this without duplicating a
> > lot of work (ie, without respecifying all the finite element on each
> > convex). Is there a way to avoid this?
> >
> > regards,
> > Cédric
>
> ok, it seems to work (at least it does not assert) if I create a fake
> fem mesh mf2 using the same linked mesh as #1 but without seting fem
> element on it. But I am not sure this is valid, or if it does what I want.
>
>    getfem::generic_assembly assem;
>    assem.push_mi(fm.GetIntegrationMesh());
>    assem.push_mf(fm.GetShapeMesh());
>    getfem::mesh_fem mf2(fm.GetShapeMesh().linked_mesh(),3);
>    assem.push_mf(mf2);
>    std::vector<T> tmpve(1,m_coef);
>    assem.push_data(tmpve);
>    assem.push_data(m_speed);
>    assem.push_mat(fm.GetAMatrix());
>    // warning: non symetric!!
>    // row/column major... check the order of data$2
>    assem.set("F=data(1);G=data$2(qdim(#2),#1);
> M$1(#1,#1)+=comp(Base(#1).Grad(#1).Base(#1))(i,:,k,:).G(k,i).F(p)");
>    assem.assembly();

You can avoid the use of a suplementary mesh_fem using mdim (mesh dimension) 
if it coincides:

 assem.set("F=data(1);G=data$2(mdim(#1),#1);
  M$1(#1,#1)+=comp(Base(#1).Grad(#1).Base(#1))(i,:,k,:).G(k,i).F(p)");

or explicitely

 assem.set("F=data(1);G=data$2(3,#1);
  M$1(#1,#1)+=comp(Base(#1).Grad(#1).Base(#1))(i,:,k,:).G(k,i).F(p)");

if your data is a 3-dimensional vector field.


Yves.



-- 

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

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