It's a little bit unreasonable to even expect funm to give accurate results for non-diagonalizable inputs, given that you're effectively asking it to compute numerical derivatives (e.g., for a 2-by-2 ...

📚 The doc issue Document spectral norm support on non-diagonalizable inputs. The spectral norm implementation(s) rely upon a power iteration which doesn't guarantee a correct result for non-diagona ...