[Gmsh] Overlapping elements in 2D mesh

[Min Yan]

Dear all,

I have noticed the 2D algorithm in Gmsh (version 1.65, compiled from SOURCE
on a Redhat Linux) sometimes generates a couple of weired elements at
certain mesh positions, primarily near to the material interface. In simple
words, some of the triangles are overlapping. Examples are attached . Such
meshes fails my eigensolver from converging. Any clue?

Additional parameters:
Mesh.Algorithm=1;
Mesh.Smoothing=6;
Mesh.ElementOrder=2;

I have also tried to use Mesh.Algorithm=3. It does not seem to have such
problem. However, I have not figured out how to make the output mesh by
Triangle look as good as that generated by Algorithm 1.

And very strangely, with exactly the same .geo file, the mesh generated
with  the PRE-COMPILED  Windows Gmsh does not have such defects.

Defects aside, the Windows-generated mesh usually have slightly more number
of nodes than the Linux-generated mesh  (by 0.14% in one of my cases). Any
explanation will be appreciated.

Thanks.

Min Yan
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