[Gmsh] Problem trying to remove a surface with gmsh; bug?

[Christophe Geuzaine]

> On 10 Oct 2017, at 23:40, joel gervais <jg95130 at yahoo.com> wrote:
> 
> Dear Christophe,
> 
> Thanks for this great software.
> Some .geo files I wrote many weeks ago lead to errors with the new version 3.0.5 of gmsh.
> It seems that something has changed between version 2.8.4 and 3.0.5 on windows 7 64 bits concerning the substract "-=" command.
> I've attached 2 pictures and the geo file (1 picture from gmsh 2.8.4 and the second from gmsh3.0.5)
> 

In Gmsh 2.x the "CombinedBoundary" operator did not correctly return the sign of the boundary entities for volumes (as it did with surfaces). This has been fixed in Gmsh 3.

In your script you should thus replace

  Skin_E[]= CombinedBoundary{Volume{VolE[]};};

with

  Skin_E[]= Abs[CombinedBoundary{Volume{VolE[]};}];

which will work in both Gmsh 2 and 3.

Christophe


> The geo file builds a simple cylinder using an extrusion,and I try to remove the initial face to keep the rest of the cylinder's skin.
> 
> Regards
> 
> Joel
> <test.geo><SkinE_gmsh284.png><SkinE_gmsh305.png>_______________________________________________
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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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