Dear Simone,
I do not understand well your problem. In GetFEM++, there
is no guaranty of a certain correspondence between dof
enumeration and element indices or vertex indices. The
correspondence can be retrieved via the methods
mf.ind_basic_dof_of_element(cv). Moreover, if I understand
well you compute a mass matrix between a P1 and a
P0 fem. In what sense do you expect a symmetry of this
matrix ?
Note that in the stable releases of Getfem, the order for
scanning the elements for dof enumeration follows a
Cutill-Mc Kee algorithm. By default, this is no longer the
case with the svn version. However, it is quite dangerous
to expect a priori a certain correspondence between dof
indices and mesh element indices.
Best regards,
Yves.
Le 25/10/2016 à 16:55, Simone Di Gregorio a écrit :
>
> Dear GetFem++ users,
>
>
> I found a problem regarding the resolution of a fem problem. I must
> solve a 1D-network in terms of pressure and velocity. I have a 1-D
> network whose mesh structure, made with regions, is like below
>
>
> BEGIN MESH STRUCTURE DESCRIPTION
>
> CONVEX 0 'GT_PK(1,1)' 0 1
> CONVEX 1 'GT_PK(1,1)' 1 2
> CONVEX 2 'GT_PK(1,1)' 2 3
> CONVEX 3 'GT_PK(1,1)' 4 5
> CONVEX 4 'GT_PK(1,1)' 5 6
> CONVEX 5 'GT_PK(1,1)' 6 3
> CONVEX 6 'GT_PK(1,1)' 3 7
> CONVEX 7 'GT_PK(1,1)' 7 8
> CONVEX 8 'GT_PK(1,1)' 8 9
>
> END MESH STRUCTURE DESCRIPTION
> BEGIN REGION 0
> 0 1 2
> END REGION 0
> BEGIN REGION 1
> 3 4 5
> END REGION 1
> BEGIN REGION 2
> 6 7 8
> END REGION 2
>
>
> I use this part of code to obtain mesh_fem:
>
>
> // pf_Uvi is 'FEM_PK(1,1)' ;
> //pf_coefvi is 'FEM_PK(1,0)';
> //meshv is the mesh described before;
> //nb_branches=3;
>
> for(size_type i=0; i<nb_branches; ++i){
>
> mesh_fem mf_tmp(meshv);
> mf_tmp.set_finite_element(meshv.region(i).index(), pf_coefv);
> mf_coefvi.emplace_back(mf_tmp);
> mf_tmp.clear();
>
>
> mesh_fem mf_tmp1(meshv);
> mf_tmp1.set_finite_element(meshv.region(i).index(), pf_Uv);
> mf_Uvi.emplace_back(mf_tmp1);
> mf_tmp1.clear();
> }
>
> It usually works well for various meshes but in this case in the
> REGION 1 the dof enumeration of mf_Uvi is wrong, in fact it comes out
> like:
>
> BEGIN MESH_FEM
>
> QDIM 1
> CONVEX 3 'FEM_PK(1,1)'
> CONVEX 4 'FEM_PK(1,1)'
> CONVEX 5 'FEM_PK(1,1)'
> BEGIN DOF_ENUMERATION
> 3: 3 2
> 4: 2 0
> 5: 0 1
> END DOF_ENUMERATION
> END MESH_FEM
>
> So the Dof enumeration is 3 2 2 0 0 1 while in all other branches
> is 0 1 1 2 2 3.
>
> While for mf_coefvi in REGION 1 the dof enumeration is in descending
> order instead of being in ascending order. (So it is 2 1 0 instead of
> 0 1 2)
>
> BEGIN MESH_FEM
>
> QDIM 1
> CONVEX 3 'FEM_PK(1,0)'
> CONVEX 4 'FEM_PK(1,0)'
> CONVEX 5 'FEM_PK(1,0)'
> BEGIN DOF_ENUMERATION
> 3: 2
> 4: 1
> 5: 0
> END DOF_ENUMERATION
> END MESH_FEM
>
>
> The problem is not only here, but also if I use this mesh_fem to build
> the mass matrix, it results to be not symmetric.
>
> //descr.IM_TYPEV='IM_GAUSS1D(6)'
>
> pintegration_method pim_v = int_method_descriptor(descr.IM_TYPEV);
> mimv.set_integration_method(meshv.convex_index(), pim_v);
> getfem::asm_mass_matrix_param(M, mimv, mf_Uvi[1], mf_coefvi[1],
> coef, meshv.region(1));
>
> Moreover, also the results of the fem problem are completely wrong.
> Instead I noticed that modifying the convex of REGION 1 of the mesh in
> this way (inverting the node numbers):
>
> CONVEX 3 'GT_PK(1,1)' 3 6
> CONVEX 4 'GT_PK(1,1)' 6 5
> CONVEX 5 'GT_PK(1,1)' 5 4
>
> I obtain:
> - a correct Dof Enumeration:
> BEGIN DOF_ENUMERATION
> 3: 0 1
> 4: 1 2
> 5: 2 3
> END DOF_ENUMERATION
> - a symmetric mass matrix
> - a correct solution in terms of velocity
> but a wrong solution in terms of pressure (maybe for the boundary
> conditions).
> So I would to know if it is possible to solve the problem and what
> could be the reason of this error.
>
> Best regards,
>
> Simone Di Gregorio
>
>
>
>
>
>
> _______________________________________________
> Getfem-users mailing list
> [email protected]
> https://mail.gna.org/listinfo/getfem-users
--
Yves Renard ([email protected]) 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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