Lyapunov-based proof of Jury - Lee´s criterion: Some appraisals

This note presents some observations concerning the question of proving (using a Lyapunov function) the well-known Jury-Lee´s absolute stability criterion for Luré type discrete-time systems with sloperestricted nonlinearity. Specifically, the inaccuracies of a previously reported Lyapunov approach to account for the sector as well as slope informations of the nonlinearity are pointed out. An alternative Lyapunov approach that correctly leads to Jury-Lee´s criterion is discussed.