Re: [Getfem-users] gf_global_function Matlab interface.

[Yves Renard]

Dear Ronan,

You have to define both the two level-set functions. A levelset object can 
contain in fact two level-set functions. This is due to the fact that the goal 
was to model a crack geometry. The first level-set describe the geometry of the 
crack and the second one the crack front (the intersection of the two level-
set is the crack front). This is rather standard. The two level-set functions 
have to be such that the iso-values are nearly orthogonal and define a system 
of coordinate. So x,y is defined relatively to this system of coordinate whan 
level-set are used.

Moreoever, you have to replace 'outside' by 'inside' in your mesh_im (and in 
fact you can use a regular integration method in your case). this gives:


m = gfMesh('cartesian', 0:1, 0:1); % Unit square with only one element.
gf = gfGlobalFunction('parser', '1'); % Global function is 1.
ls  = gfLevelSet(m, 1, 'x-2', 'y-2');
mls = gfMeshLevelSet(m);
mls.set('add', ls);
mfg = gfMeshFem('global function', m, ls, {gf});
mim = gf_mesh_im(m, gf_integ('IM_QUAD(3)'));
volume = gf_asm('volumic', m.get('cvid'), 'V(#1)+=comp(Base(#1))(:)', mim, 
mfg);



But of course, you are right, it should be possible to use it without a level-
set (but this is not possible for the moment even in the c++ code). In fact it 
would be sufficient to define a "global_function_not_on_levelseté similar to 
"global_function_on_levelset" in getfem_mesh_fem_global_function.cc and 
interface it in gf_mesh_fem.cc.


Yves.







On jeudi 14 octobre 2010, Ronan Perrussel wrote:
> Dear getfem users,
> 
> I am still trying to use gf_global_function with the Matlab interface.
> It seems not possible to use gf_global_function under the Matlab
> interface without using  levelset (but it is possible in C++) and I try
> to understand how it works.
> 
> I try a (new) stupid example to understand :
> m = gfMesh('cartesian', 0:1, 0:1); % Unit square with only one element.
> gf = gfGlobalFunction('parser', '1'); % Global function is 1.
> ls  = gfLevelSet(m, 1);
> ls.set('values', 'x-2.'); % With this levelset p(x, y) < 0 inside the
> domain.
> mls = gfMeshLevelSet(m);
> mls.set('add', ls);
> mfg = gfMeshFem('global function', m, ls, {gf});
> mils = gf_mesh_im('levelset', mls, 'outside', gf_integ('IM_QUAD(3)'));
> volume = gf_asm('volumic', m.get('cvid'), 'V(#1)+=comp(Base(#1))(:)',
> mils, mfg); % I integrate my global function over the whole domain.
> 
> As my global function is 1 over the domain (and the mesh contains only
> one element), I thought that I would obtain the area of the domain but I
> just got zero. What is wrong?
> 
> Thank you in advance for your advice,
> Best regards,
> Ronan


-- 

  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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