Stability of lead modes calculation
While Schur decomposition works well in general, it seems to fail for some Hamiltonians. The example people encounter most frequently is Kane-Mele model on a zigzag ribbon at zero energy. Another important example is Kwant_QZ_iteration_failed.ipynb because that system fails at many different energies. Maximilian Trescher reported this issue over here
It isn't at all obvious whether we can improve on stability in these cases, but identifying what happens would also be important.