Add Dofs.get_element_dofs

[kinnala]

This was a feature request from @ahhuhtal . The use case would be to figure out what degrees-of-freedom correspond to a named subdomain.

[gdmcbain]

Like in the example of the insulated wire?

https://github.com/kinnala/scikit-fem/blob/9c485745018a915ae683295a011f910228741352/docs/examples/ex26.py#L38

[kinnala]

Yeah, I see your point: why have a separate function if it can be done in one line?

Well, in principle, get_element_dofs could work also with function handles and so on. But the real reason for introducing Dofs objects was to have a single place for different methods that fetch DOF's. So maybe instead of making new multitype methods, we simply add multiple methods to Dofs? Such as

• Dofs.element_dofs_byindex
• Dofs.element_dofs_byhandle
• Dofs.element_dofs_bytag

and so on.