[Dune] Handling several materials

[Christian Engwer]

> In case of adaptative remeshing, would those modules update individual domains, so I
> would not have to care about those technicalities you mentionned ?

If you use local adaptivity you will always have to make sure your
data is present on the adapted mesh. Usually this requires some
interpolations and so on. In a similar way we now also have to
transfer these indices. And additionaly from the "Gmsh" mesh to your
actual mesh object.

If you would opt for multidomain or subgrid. Things wuld be
significantly more complecated. You would safe some work, because you
don't transfer the parameters between meshes (as you have exactly one
parameter set per subdomain), but you will have to setup Problems mit
many different subdomains and extract the list of cells in one
subdomain from your gmsh file (so you will need again the initial
indices).

Ciao
Christian