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## Re: [Getfem-users] Data for piecewise constant coefficients

 From: Jehanzeb Hameed Subject: Re: [Getfem-users] Data for piecewise constant coefficients Date: Wed, 8 Jul 2009 11:03:23 -0500

```Is there a simple way in getfem to map points to convexes, that is:

> the interpolation point for each element is the barycenter. So you
> can discriminate in wich part of your domain is the point.

Given the particular barycenter, say 'b', do I have to build a list of
all barycenters in the beginning, and then search for 'b' in that
list? Or is there some already builtin way to go about it.

Thanks,
-Jehanzeb

On Wed, Jul 8, 2009 at 4:50 AM, Yves Renard<address@hidden> wrote:
> On mardi 7 juillet 2009, Jehanzeb Hameed wrote:
>> Hello,
>>
>> In laplacian.cc  "getfem::classical_fem(pgt,0))" is used to represent
>> the fem space for coefficient function (mf_coef). This coefficient
>> function is constant on each convex. It is not used in laplacian.cc,
>> and is set to one by creating a vector ones (
>> std::vector<scalar_type>(mf_coef.nb_dof(), 1.0) ).
>>
>> Now say, I want to this coefficient to be piecewise constant, that is
>> constant on each of (say two) subdomains. It seems I cant use
>> interpolation for it, as interpolation functions use coordinates of
>> points, and dont seem to indicate which convex they come from.
>
> Indeed you can. If you represent your coefficient on a P0 method (piecewise
> constant), the interpolation point for each element is the barycenter. So you
> can discriminate in wich part of your domain is the point. If you want to
> fill the corresponding vector by hand, you can use the method
> mf.point_of_dof(i) for the P0 method which will give you the coordinates of
> the corresponding barycenter. Otherwise, you can also use the interpolation
> functions.
>
> Yves.
>
>> One way
>> I can think of doing it, is to loop for mesh convexes, look up which
>> region the convex belongs to, and then set the corresponding entry in
>> the coefficient vector. However I am not sure if this is the way to
>> go, as numbering of convexes in the mesh  may not correspond to
>> numbering of dof's of the vector passed as data for assembly.
>>
>> Is the above method the one to use, or is there a more elegant way around
>> this?
>>
>> Thanks,
>> -Jehanzeb
>>
>> _______________________________________________
>> Getfem-users mailing list
>> https://mail.gna.org/listinfo/getfem-users
>
>
>
> --
>
>  Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
>  Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
>  20, rue Albert Einstein
>  69621 Villeurbanne Cedex, FRANCE
>  http://math.univ-lyon1.fr/~renard
>
> ---------
>

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