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 Dear Phuoc, Yes, the export can also have some problems with the singular transformation ... I robustified a bit the evaluation. Can you try ? Best regards, Yves Le 19/06/2018 à 12:48, Huu Phuoc BUI a écrit : Dear Yves, I now faced with mixed elements of higher order. In the enclosed script, I use degree = 2 for all elements, and set the integration method mim = gf.MeshIm(m, 8), but after resolution, there are 'nan' values in displacement filed. The 'nan' values are shown by yellow color in Paraview as I tried to change the order for integration method but without success. Please let me know if you have an idea. Thanks a lot. Best regards, Phuoc On 19/06/2018 10:21, Huu Phuoc BUI wrote: Dear Yves, Thanks a lot for your help. I think the fact that assigning the integration method by only providing the degree of interpolation is very useful. That solved my problem now. Thank you also for your remark about using macro for models. It's really helpful. Best regards, Phuoc On 18/06/2018 17:32, Yves Renard wrote: Dear Phuoc, The main reason is that you use a Newton-Cotes integration methods on the prism. The Newton-Cotes integration method has Gauss points on the geometrical nodes which is not convenient at all for the pyramid. You can use instead mim = gf.MeshIm(m, 3) which will select an integration of order at least 3 on each element. Just an additional remark. You can use the macro system which can give clearer expressions. For instance sig_u = "(lambda_para*Trace(Grad_u)*Id(qdim(u)) + mu_para*(Grad_u + Grad_u'))" stress_jump_inner = "{sig_u} .... ".format(sig_u=sig_u) can also be entered has md.add_macro('sig_u',  "(lambda_para*Trace(Grad_u)*Id(qdim(u)) + mu_para*(Grad_u + Grad_u'))") stress_jump_inner = "sig_u ... " or stress_jump_inner = "Def sig_u := (lambda_para*Trace(Grad_u)*Id(qdim(u)) + mu_para*(Grad_u + Grad_u')); sig_u ..." you can also define macros with parameters, see http://getfem.org/userdoc/gasm_high.html#macro-definition Best regards, Yves Le 18/06/2018 à 13:35, Huu Phuoc BUI a écrit : Dear Yves, Please find enclosed the smallest python script. I made an mistake when assigning Lamé coefficients for 3D problems (sorry!). Now the problem seems to be different than the 'nan' ouput. By using generic assembly, it says: "RuntimeError: (Getfem::InterfaceError) -- Error in bgeot_geometric_trans.cc, line 245 bgeot::scalar_type bgeot::lu_inverse(bgeot::scalar_type*, bgeot::size_type, bool): Non invertible matrix " Best regards, Phuoc On 18/06/2018 10:57, Yves Renard wrote: Dear Phuoc, Do you compute some gradient quantities on the finite element nodes ? If not, it should not pose any problem since using the generic assembly, the computation are located on the Gauss points which are not located on the nodes. can you extract the smallest possible program on which the error occurs ? Best regards, Yves Le 18/06/2018 à 10:35, Huu Phuoc BUI a écrit : Dear Yves, Sorry I email you again on this topics. In fact, the generic assembly did some computation on pyramid elements but the output is 'nan'. On elements of others types (of the mixed mesh), the output is fine. Please let me know if you have an idea. Thanks. Best regards, Phuoc On 15/06/2018 16:43, Huu Phuoc BUI wrote: Dear Yves, That's great! It's indeed working now. Thank you very much for your help. Best regards, Phuoc On 15/06/2018 16:38, Yves Renard wrote: Dear Phuoc, The problem is indeed the same, to compute the location of gauss points on a neighbour element, the inversion of the geometric transformation is called. This inversion used a Newton algorithm whose starting point is a node of the element ... (function find_initial_guess in bgeot_geotrans_inv.cc). I changed a bit the starting point, so it should work now. But this is clear that the fact that the transformation is singular at the pyramid tip is a difficulty. Best regards, Yves Le 15/06/2018 à 11:53, Huu Phuoc BUI a écrit : Dear Yves, Thank you very much for your help. Now it worked when computing the outer faces. But I faced another problem of this mixed mesh. In fact, I'd like to compute the stress jump at the inner faces using generic assembly, and GetFEM++ showed an error like this: "   File "/usr/local/lib/python2.7/dist-packages/getfem/getfem.py", line 5591, in asm_generic     return getfem('asm', 'generic', mim, order, _expression_, region, model, *args) RuntimeError: (Getfem::InterfaceError) -- Error in getfem_generic_assembly_compile_and_exec.cc, line 3887 virtual int getfem::ga_instruction_neighbour_transformation_call::exec(): Geometric transformation inversion has failed in neighbour transformation " So, as you said, this error comes from geometric transformation of pyramid elements. Do you have an idea how to fix it? Best regards, Phuoc On 15/06/2018 11:10, Yves Renard wrote: Dear Phuoc, The problem come from the fact that the test is made on the mean unit normal vector on a face. This mean unit normal vector is computed by averaging the unit normal vector on each geometrical node of a face. Unfortunately, for a pyramid element, the transformation is singular on the geometrical nodes. I replaced the mean of normal vector by the normal vector on the mean of geometrical nodes of the face. It fixes the problem.  (I push the change on the master branch). Best regards, Yves Le 14/06/2018 à 15:40, Huu Phuoc BUI a écrit : Dear Yves, Please find the mesh attached. Thank you for your help. Best regards, Phuoc On 14/06/2018 14:52, Yves Renard wrote: Dear Phuoc, No, I see no reason. If you can just send me the mesh in a format readable by GetFEM, I could check what is wrong. Best regards, Yves Le 14/06/2018 à 10:24, Huu Phuoc BUI a écrit : Dear Getfem-users, I have a problem with computing the outer faces when using a mixed mesh (having tetras, hexa, prisms and pyramids). The error is: face_left = m.outer_faces_with_direction([0, 0., -1.0], 0.01)   File "/usr/local/lib/python2.7/dist-packages/getfem/getfem.py", line 1372, in outer_faces_with_direction     return self.get("outer_faces_with_direction", v, angle, CVIDs)   File "/usr/local/lib/python2.7/dist-packages/getfem/getfem.py", line 1152, in get     return getfem('mesh_get',self.id, *args) RuntimeError: (Getfem::InterfaceError) -- Error in bgeot_geometric_trans.cc, line 381 const base_matrix& bgeot::geotrans_interpolation_context::B() const: Non invertible matrix Please let me know if you have any idea. Thank you. Best regards, Phuoc ```-- 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 --------- ``` ```-- 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 --------- ``` ```-- 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 --------- ```