[Gmsh] "Perfect Match Failed" Problem with Blossom

[Christophe Geuzaine]

Hi Johannes,

That's weird - it seems to work fine over here (cf screenshot). I will test it on our Linux machine when I have the time.

Does it happen with all the triangulation methods (MeshAdapt, Delaunay, Frontal, Delaunay for quads)?


Christophe


On 13 Mar 2013, at 13:32, Johannes Reinhardt <johannes.reinhardt at unifr.ch> wrote:

> Hello everybody,
> 
> first I want to thank everybody involved in the development of gmsh. It is a really great tool and has helped me a lot in my research.
> 
> However I run into a probem when I try to create a 2D quad mesh with the outline of two superimposed disks embedded. However Blossom almost always fails with the message:
> 
> Warning : Perfect Match Failed in Quadrangulation, Applying Graph Splits
> 
> printed 10 times. I attached a simple geometry file that shows this problem.
> 
> For small distances (e.g. dist=2.1) this problem does not occur, but for larger distances (and these are the ones that I want to study), I always get this error.
> 
> For other geometries where I had this problem, playing a bit with the mesh element sizes helped, but I could not find good numbers for this case. I also tried both DelQuad and MeshAdapt as Meshing Algorithms, but I always get the error above.
> 
> I briefly looked at the Blossom Quad publication, but could not find any explanation for this behaviour. My best guess is, that the embedded curve conflicts with a perfect matching, and the extra edges mechanism fails in this case.
> 
> I tested both gmsh 2.6.1 compiled from source and the precompiled gmsh 2.7.0 Linux 64bit binary on Ubuntu 11.10, both show the same behaviour.
> 
> Has anybody an idea how to reformulate the geometry description to avoid this problem?
> 
> Thanks in advance and greetings
> 
> Johannes
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine



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