[Gmsh] Surface numbering from extrude

[Christophe Geuzaine]

Manav Bhatia wrote:
> Hi
>   For the following input,
> 
> Point(10) = {0,0,0,.1};
> Extrude Point {10,{1,0,0}};
> Extrude Line {1, {0,1,0}};
> 
> 
> For a surface made from extrusion of a line, the surface number  
> should ideally be the number obtained from 'newl'. (This is the  
> procedure for point and surface extrusions  to get line and volume  
> respectively). Hence the surface number for the file given above  
> should be 1. However, I get the number as 5. I tried similar  
> examples, and found that the surface number is obtained as 'newl'. Is  
> this a bug?
> How are surfaces numbered for surfaces made from line extrusions?
> 

We keep this numbering for backward compatibility with old .geo files. 
To get the new (more "natural") numbering, just add

Geometry.OldNewReg=0;

at the beginning of your model or in your option file.

Still, usually it's better to use the numbers returned by the commands 
themselves. See e.g. tutorial/t2.geo or tutorial/t3.geo.


> Thanks
> Manav
> 
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-- 
Christophe Geuzaine
Assistant Professor, Case University, Mathematics
http://www.case.edu/artsci/math/geuzaine