[Gmsh] curved mesh and jacobian

[Christophe Geuzaine]

> On 4 Nov 2020, at 09:31, françois fraysse <francois.fraysse at hotmail.fr> wrote:
> 
> Many thanks for your answer,
> 
> In the meanwhile I found one of your articles which explains bounds for triangles:
> 
> https://gmsh.info/doc/preprints/gmsh_curved2_preprint.pdf
> 
> Then, after digging more in my own code I found a mistake related with node numbering, I was using vtk ordering for 10 node tets which is slighty different (2 last mid-edges nodes are swapped). That did it. 
> 

Ok, great!

Christophe


> My apologies...
> 
> btw AnalyseMeshQuality returns minJ inside or very close to target
> 
> Best regards 
> De : Christophe Geuzaine <cgeuzaine at uliege.be>
> Envoyé : mercredi 4 novembre 2020 08:10
> À : françois fraysse <francois.fraysse at hotmail.fr>
> Cc : gmsh at onelab.info <gmsh at onelab.info>
> Objet : Re: [Gmsh] curved mesh and jacobian
>  
> 
> 
> > On 29 Oct 2020, at 17:49, françois fraysse <francois.fraysse at hotmail.fr> wrote:
> > 
> > Hello GMSH users and developers,
> > 
> > I generated a simple quadratic tetrahedra based mesh using default settings with gmsh v4.6.0. After regularizing, minimum jacobian lies between default target, ScaledMinjac=0.102 so mesh seems valid, no warning or errors.
> > 
> > Then in a separate code I post-process the mesh and build quadratic shape functions. I evaluate the determinant of the Jacobian at the 10 nodes of each tetra and it turns out that I get some small values below zero for some tetras : ~1e-2/1e-3.   
> > 
> > I do not exclude a mistake in the verification procedure, but I didn't find it so far. 
> > 
> > My question is : is ScaledMinJac an exact value or an approximation ? 
> > 
> 
> The value is not exact, but the validity check is a provable bound, i.e. we we report that the element is correct it should be. Can you run the AnalyseMeshQuality plugin and check the results?
> 
> Christophe
> 
> 
> > Thank you for developing such a great software :) 
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> 
> — 
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science 
> http://people.montefiore.ulg.ac.be/geuzaine

— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://people.montefiore.ulg.ac.be/geuzaine