[Gmsh] Strange differences between Gmsh 2.2.3 and 2.2.4

[Christophe Geuzaine]

Moritz Nadler wrote:
> I made a .geo file with gmsh 2.2.3 until it produced a mesh a 
> approximately representing what I had in mind. But when I used the same 
> geo file with gmsh 2.2.4 I got a totally different mesh ( well the 
> geometry remains the same but the mesh density globally and locally 
> different. See these gmsh terminal output for a first idea.
> 
> Both versions were compiled from source with GCC.
> 
> 
> Gmsh version 2.2.3
> 
> gmsh -rand 1.e-8 circle2.geo -2
> Info    : 'gmsh -rand 1.e-8 circle2.geo -2' started on Thu Sep 25 
> 19:02:26 2008
> Info    : Reading 'circle2.geo'
> Info    : Read 'circle2.geo'
> Info    : Meshing 1D...
> Info    : Meshing curve 1 (Line)
> Info    : Meshing curve 2 (Line)
> Info    : Meshing curve 3 (Line)
> Info    : Meshing curve 4 (Line)
> Info    : Meshing curve 5 (Line)
> Info    : Meshing curve 6 (Line)
> Info    : Meshing curve 7 (Line)
> Info    : Meshing curve 8 (Line)
> Info    : Meshing curve 9 (Line)
> Info    : Meshing curve 10 (Line)
> Info    : Meshing curve 11 (Line)
> Info    : Meshing curve 12 (Line)
> Info    : Meshing curve 13 (Line)
> Info    : Meshing curve 14 (Line)
> Info    : Meshing curve 15 (Line)
> Info    : Meshing curve 16 (Line)
> Info    : Meshing curve 100 (Circle)
> Info    : Meshing curve 200 (Circle)
> Info    : Mesh 1D complete (0.504031 s)
> Info    : Mesh
> Info    : Meshing 2D...
> Info    : Meshing surface 106 (Plane, MeshAdapt+Delaunay)
> Info    : Mesh 2D complete (65.8241 s)
> Info    : Mesh
> Info    : 107605 vertices 215214 elements
> Info    : Writing 'circle2.msh'
> Info    : Wrote 'circle2.msh'
> 
> 
> Gmsh version 2.2.4:
> 
> gmsh -rand 1e-8 circle2.geo -2
> Info    : Reading 'circle2.geo'
> Info    : Read 'circle2.geo'
> Info    : Meshing 1D...
> Info    : Meshing curve 1 (Line)
> Info    : Meshing curve 2 (Line)
> Info    : Meshing curve 3 (Line)
> Info    : Meshing curve 4 (Line)
> Info    : Meshing curve 5 (Line)
> Info    : Meshing curve 6 (Line)
> Info    : Meshing curve 7 (Line)
> Info    : Meshing curve 8 (Line)
> Info    : Meshing curve 9 (Line)
> Info    : Meshing curve 10 (Line)
> Info    : Meshing curve 11 (Line)
> Info    : Meshing curve 12 (Line)
> Info    : Meshing curve 13 (Line)
> Info    : Meshing curve 14 (Line)
> Info    : Meshing curve 15 (Line)
> Info    : Meshing curve 16 (Line)
> Info    : Meshing curve 100 (Circle)
> Info    : Meshing curve 200 (Circle)
> Info    : Mesh 1D complete (0.43 s)
> Info    : Mesh
> Info    : Meshing 2D...
> Info    : Meshing surface 106 (Plane, MeshAdapt+Delaunay)
> Info    : Mesh 2D complete (365.69 s)
> Info    : Mesh
> Info    : 750256 vertices 1500535 elements
> Info    : Writing 'circle2.msh'
> Info    : Wrote 'circle2.msh'
> 
> 
> My questions are:
> Can somebody tell me the reason for this?
> Did the syntax change so that what I was using is not longer valid in 
> 2.2.4?
> Is there a Bug responsible for this. And if in which version?
> 
> Can somebody reproduce my findings ( I attached the .geo file )?
> Or must be something wrong with my installation. ( although I could 
> reproduce this already on 2 machines).

Hi Moritz - In 2.2.3 we assumed that when you used Fields, you never 
wanted to extend the element sizes from the boundary into the interior. 
This was OK if you only had Fields, but prevented a mixture of Fields + 
mesh sizes prescribed at geometry vertices and/or according to curvature.

2.2.4 removes this assumption and lets you control everything. In your 
case if you do not want to extend the sizes from the boundary, just set

Mesh.CharacteristicLengthExtendFromBoundary = 0;

in your .geo file. This should get the "old" mesh back.



> 
> 
> kind regards
> 
> 
> Moritz
> 
> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine