@miles maybe with a large enough setting of tol it normally just builds two or three Krylov vectors anyway, but then maybe builds more for trickier cases like criticality “automatically” (obviously we would have to experiment with that).
@lkdvos that’s an interesting suggestion to default to ishermitian=false. My first reaction would be that it may just hide real user issues, like if they input an incorrect Hamiltonian that is accidentally non-Hermitian, but probably they would find out anyway in one way or another (like with complex energies…). Also, users should really be testing their Hamiltonians/MPOs out on small systems with ED.