[Gmsh] file format

[oka]

Dear Rui Maciel,

Thank you so much for quick response.
4 5 0 1 2 1 -4 
about 1 2 1 -4, manual has no explanation.
I guess
2 means this mesh in overlap region
1 means partition number
-4 means overlap facing opposite mesh number (4)
Is this true ?

Best regards,

Oka

> 
> oka wrote:
> > Dear developer,
> > 
> > I am not familiar with gmsh file format.
> > In my partitioed mesh case,
> > One file (total 4 partitions) shows as follows.
> > - - - -
> > 21586 4 4 0 1 1 1 790 148 5726 6827
> > 21587 4 5 0 1 2 1 -4 5004 1004 4710 7455
> > 21588 4 4 0 1 1 1 3280 2145 3283 8302
> > - - - -
> > For example. for element number 21587,
> > what is the meaning of following numbers,
> > 5 0 1 2 1 -4
> > especially, why extra -4 appears although other
> > elements has no minus values ?
> > 
> > Best regards,
> > 
> > Oka
> 
> It may not be of much help but nonetheless here's my 0.02?.
> 
> The format which was implemented for the element definition field consists 
> basically of the following four non-terminal fields:
> 
> <element-number> <element type> <element tags> <element nodes>
> 
> 
> focusing on the <element tags> field, it basically follows the following 
> format:
> 
> <element tags number> <element tag>+
> 
> 
> To put it in other words, it consists of a leading integer ( indicating how 
> many tags there are) followed by that many tags.  So, considering your element 
> number 21587, the <element tags> field of that element includes the following 
> tokens:
> 
> 5 0 1 2 1 -4
> 
> 
> That is, the <element tags number> is 5, followed by 5 tags.  As your <element 
> type> tag is 4, it means that that particular element is a 4-node tetrahedron.  
> As a consequence, you will notice that after the mysterious -4 token you will 
> find the following tokens:
> 
> 5004 1004 4710 7455
> 
> 
> Those 4 integer tokens are the 4 references to the nodes which are used to 
> define that particular element.
> 
> One of the tricky things about the MSH ASCII file format is that it isn't 
> thoroughly defined in the specification presented in Gmsh's documentation[1].  
> In fact, I believe that only the first 3 tags are defined.  Moreover, according 
> to that specification you shouldn't get any negative number as a tag.  So this 
> is a weird one.  
> 
> Nonetheless, the good news about this is that you can simply ignore that tag, 
> possibly without any practical consequence.  You still get your mesh and you 
> still get a hand-full of tags which you may or may not use (reference to a 
> physical entity, geometrical entity and mesh partition).  If you weren't 
> expecting to get more information from that mesh then you can pretty much 
> ignore everything else and you won't miss any information.
> 
> 
> Hope this helps,
> Rui Maciel
> 
> [1] http://www.geuz.org/gmsh/doc/texinfo/gmsh.html#MSH-ASCII-file-format
> 
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-- 
oka <oka at bpe.es.osaka-u.ac.jp>