[Gmsh] Questions on 4.1 format

[Christophe Geuzaine]

> On 30 Mar 2020, at 16:51, paul francedixhuit <paul18fr at gmail.com> wrote:
> 
> Hi All
> I'm currently having a look to the new 4.1 gmsh format.
> 
> Compared to the previous 2.2 legacy one:
> 	• I guess $Nodes and $Elements for example use now blocs (or it has been splitted in blocs) in order to take advantages of parallelization, hasn't it?

It allows that, yes. It also allows for much more efficient reading from/writing to disk.

But more fundamentally, the new format reflects the underlying Gmsh data model (http://gmsh.info/doc/texinfo/gmsh.html#Gmsh-API), and it contains all the information needed by Gmsh to save/reload a model without information loss.

> 	• $Entities and $PhysicalNames are used to define specific groups of elements to apply on specific features (typically sub-parts)

Entities contain the underlying (topological) boundary representation of the Gmsh model. Physical groups are just groups of entities. They are defined even without a mesh. Mesh nodes/elements are stored in the model entities.

Note that the only two fields that are necessary in a simple MSH file are $Nodes and $Elements. All the rest is useful for Gmsh - but can be omitted by other codes if they don't need the additional topological model information.

> Nonetheless concerning $NodeData (and $ElementNodeData), I've not tested it so far but I feel the structure remains identical to the 2.2 one: am I right? if so I can imagine improvements will be provided in a next future, won't be?
> 

Yes indeed. See the end of the http://gmsh.info/doc/texinfo/gmsh.html#MSH-file-format section.

> The next steps will be to use it through the Python API 😊

The Python tutorial is now on par with the GEO and C++ ones: https://gitlab.onelab.info/gmsh/gmsh/-/tree/master/tutorial

New extended ("x") tutorials will be added in the near future to help new users with features that are only available through the API (and not in GEO files).

Don't hesitate to contribute your feedback on https://gitlab.onelab.info/gmsh/gmsh/-/issues/795 : we will use it to track suggestions or corrections.

Cheers,

Christophe

> 
> Bye
> 
> Paul
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— 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine