[Gmsh] possible bug in the Frontal Algo

[walter.steffe at alice.it]

In my experience I have found that the surface triangulations generated by the Frontal Algo have a high quality.
Unfortunately sometimes a face triangulation is wrong because a triangle is missing (see annexed picture).The missing triangle has always a vertex which is also a vertex of the geometrical face so that the adjiacient edges belong to a couple of different geometrical edges. 
I have seen in your code that the option ALGO_2D_FRONTAL triggers the calling of the function bowyerWatsonFrontal(..) Inside of this function there is a loop where the worst triangles gets destroyed and replaced by smaller tiangles upon the inserction ofa new point. 
I suspect that for that particular position (worst triangle has a vertex on a face vertex) the triangle is destryed but the subsequent point insertion fails.
Walter



 
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