Improve mechanism for detecting degenerate eigenvectors #14
Description
In its current form the mechanism in the solve methods of FullDiagonalization, LOBPCG and DMRG for detecting degenerate states is very limited.
It would be nice to extend this feature to also include excited states. Maybe this would involve a n_states argument which determines if only the ground state or also excited states are targeted. One possible application would be assembly strategies involving excited snapshots.