[Gmsh] curved mesh and jacobian

[Christophe Geuzaine]

> 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