[Gmsh] Physical Entities & Tags problem in output file version 2.0 !

[Christophe Geuzaine]

thierry.gilles at tiscali.nl wrote:
> --------------------------------------------------------------------------------------------------------------------------
> C.
> 
> Thank you for such a quick and helpful answer !
> Here is my feedback to your intervention :
> --------------------------------------------------------------------------------------------------------------------------
> 
> Did you check the "Save all elements" option in the dialog? You
> shouldn't: checking this will discard all the physicals. (I've changed
> the label in the cvs version to make it more explicit.)
> 
> I've attached a slightly modified .geo file as well as the resulting
> meshes. Just load one of the meshes and use "Physical" in
> Tools->Visibility to examine the physicals: they look fine to me.
> 
> ----------------------------------------------------------------------------------------------------------------------------
> Indeed I did.. and I see now how wrong it was :-!  Couldn't guess 
> actually.. Should have tried !
> 
> But still...two little questions
> Question 1)
> Can you explain why you added the Physical Volume and the Physical 
> Line ???

Because as soon as some physical entities are defined, they are the only
entities that are saved in the .msh file. So if you don't define the
volume, you will get no tets in the .msh file.

> Actually, the surfaces belong now to 3 Entities : directly to 2 
> Physical Surfaces and indirectly to 1 Physical Volume.
> But the mesh elements are repeated only twice, tagged with the 2 
> Physical Surfaces only.. Anyway, the 2 tags coming from the 2 Physical 
> Surfaces already help me..

That's the idea: using physical entities, you explicitly define the
(groups of) elementary entities that you want to save in the .msh file.
If an elementary surface belongs to 2 physical surfaces, then its
elements will be saved twice in the .msh file, once with each physical
number.

> Question 2)
> As the mesh elements are repeated in the .msh file, I wonder now if I 
> can be sure that every Surface Entity will not be meshed twice with a 
> different mesh,

Yes: the physicals only group elementary entities (and possibly change
their orientation, if you add '-' signs). They don't change anything in 
the actual mesh generation.

Best wishes,

Christophe


> leaving me with Surfaces meshed differently on both 
> sides !! This appears not to be the case in our Double Pyramid example, 
> but can I be sure of that for any Geometry ?
> 
> Thanks a lot already !
> ------------------------------------------------------------------------------------------------------------------------------------------------
> 
> Thierry GILLES
> 
> 
> 
> 


-- 
Christophe Geuzaine
Assistant Professor, Case Western Reserve University, Mathematics
http://www.case.edu/artsci/math/geuzaine