[Dune] Handling several materials

[Christoph Grüninger]

Hi Thomas,
to add another answer. You need to figure out how to tell Dune your
spacial parameter. Christian's answer is a good starting point for this.
In the long run, you will create your own tailor-made
solution that fits best for your problems and your users.

In DuMuX all spacial parameters are within a class with members for the
different physical properties. Some users only want to create
simulations, so all they need to know is how to define the spatial
parameters, boundary, and initial values (plus compiling, running, and
viewing results). More advanced users also modify the models, so they
need to know how to access the spacial parameters of the current element
from the local operator. Only a couple of people needs to understand how
both ends come together and what magic happens under the hood.

As Christian wrote, there are two directions to take:
- You define a function, lambda, etc. to translate the coordinates from
your current element to your material value
- You add IDs or parameters directly to the grid an read them in
together with your grid. From these you decide on the material value.

Bye
Christoph

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