[Gmsh] questions on the .msh-file

[Geordie McBain]

On Thu, Jan 28, 2010 at 8:04 PM, Martin Huber <mhubi87 at gmail.com> wrote:
> I'm currently working on including meshes, consisting only of 3-node
> triangles, from gmsh into a BEM-code. So I have some questions on the
> msh-file that I couldn't find in the manual:
> - In the element section there are not only 3-node triangles, but also
> some nodes and some edges (but as far as I noticed not all of them). Are
> these special nodes/edges and why are they in the elements section?

They're not necessarily special, just artifacts from how the geometry
was defined: `elementary geometric entities'.  You can suppress them
and just output the three-node triangular elements by defining the
surface they lie on as a `Physical Surface'
<http://geuz.org/gmsh/doc/texinfo/gmsh.html#Surfaces>; for the
distinction between `elementary' and `physical' entities in Gmsh, see

* http://geuz.org/gmsh/doc/texinfo/gmsh.html#Geometry-module

* http://geuz.org/gmsh/doc/texinfo/gmsh.html#Elementary-vs-physical-entities

> - Is it possible to get information about neighbourhood of the
> triangles, e.g. an additional array that tells, which triangle is beside
> the edge number i of the current triangle?

This is harder.  I don't know how to do it in Gmsh, or whether it's possible.