an.
    miter == 3:  Chord iteration with internally computed diagonal Jacobian.
    miter == 4:  Chord iteration with user-supplied banded Jacobian.
    miter == 5:  Chord iteration with internally computed banded Jacobian.

Side effects: If either self.mu or self.ml is not None and the other is None,
then the one that is None is set to 0.
Nr