Block Matrices
Problem to solve with the new feature
For handling various kinds of couplings between different physics a basic BlockMatrix class should be present (based on PETSc's MatNest)
So Basically something like
A B
C D
in the 2by2 case with A B C D being abstract matrices. The current implementation in slimfem does not provide enough abstraction to handle that (abstract_matrix is too specialized to be used for that)
Intended users
Developers, advanced users, anyone that wants to use more than one physic
Proposal
References can be found in the mfem project for example: https://github.com/mfem/mfem/blob/master/linalg/petsc.hpp