Comments on "On the robust Popov criterion for interval Lur"e systems

This paper supplements the remarks made in a paper by Dahleh et al. (IEEE Trans. Automat. Contr. vol.38, p.1400-5 (1993)) regarding the Popov sector of Lur'e systems with interval plants. A numerical example is provided to show that strict inequalities hold among three sectors: those obtained by the theorem of the paper, by applying Popov theorem to each member system, and by applying that to each of the systems with Kharitonov plants. This counterexample negates a tempting conjecture on "strong" robust Popov criterion.<
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