[Gmsh] neighbors information

[jeremy theler]

Hello all,

I remember this issue being discussed more than one year ago, but I would like 
to call it again.

When trying to use gmsh for solving a PDE problem using the finite volumes 
method, it is necessary to tell which elements (or cells) are neighbors of 
each other, i.e. to make a list of all the neighbors each element (cell) has. 
This is also true in finite element problems when the boundary condition 
depends on the properties of the material. Think, for example, aboute the heat 
conduction problem with different materials and a Neumann boundary condition 
(i.e. imposed heat flux) applied into a surface physical entity in which the 
thermal conductivity coefficient depends on the material, which in turn can be 
associated to a volumetric physical entity. To know which coefficient k to apply 
in each plane element of the boundary, the solver needs to know which is the 
volumetric element that is adjacent to the surface element containing the 
boundary condition.


For one and two-dimensional meshes, I managed to obtain the list of all the 
neighbors each element has in a .msh file using a poorly-design algorithm. I 
believe that if gmsh could make the list during the mesh generation process 
and optionally add it to the .msh file, the overall process would be more 
efficient.

I would love to hear your comments back, including using FVM with gmsh-
generated meshes.

--
jeremy