[Gmsh] Unexpected behaviour with Geometry.AutoCoherence=0 and duplicatedsurfaces.

Mark Starnes mark.starnes at fttech.co.uk
Fri Apr 30 12:46:37 CEST 2010

Hi everyone,

For various reasons, the meshes I produce use Geometry.AutoCoherence=0
to prevent the collapsing of coincident objects.  I perform collapsing
at a later point when needed.

When copying a surface, however, extra nodes seem to appear on the
duplicated surface and when meshed, Gmsh shows a Seg. Fault.  I tried
this on windows and linux, and am using version 2.5.0-svn.

The following script shows the issue.  The behaviour can be turned on or
off by commenting the Geometry.AutoCoherence=0 command:

Geometry.AutoCoherence = 0;

Point(1) = {0,0,0}; // centre
Point(2) = {1,0,0};
Point(3) = {0,1,0};
Point(4) = {-1,0,0};
Point(5) = {0,-1,0};

Circle(1) = {2, 1, 3};
Circle(2) = {3, 1, 4};
Circle(3) = {4, 1, 5};
Circle(4) = {5, 1, 2};

Line Loop(5) = {2, 3, 4, 1};
Plane Surface(6) = {5};

test[] = Translate{0,0,-0.1} {Duplicata{Surface{6};}};

I noticed this, as I have coincident faces which need identical
meshes for coupling to occur on a node to node basis between different

If anybody has a suggestion for how to match meshes on coincident but
numerically separate faces, I'd love to hear it!  Currently, all I can
think of is the Duplicata approach above.

As a side, I have just been awarded my Doctorate of Aeronautics from
Imperial College, London:  I used Gmsh throughout the project (and
referenced it as requested!), and have posted a few times, receiving
much help from the community.  So, thanks for this great software and
thanks for the support over the years!

Best regards,

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