Comments on "Two necessary conditions for a complex polynomial to be strictly Hurwitz and their applications in robust stability analysis" [with reply]

In the original paper, Y. Q. Shi, K. K. Yen, and C. M. Chen (IEEE Trans. Automat. Contr., vol. 38, no. 1, p. 125-8, 1993) present two simple necessary conditions for a polynomial with complex coefficients to be strictly Hurwitz. They claim that this is an extension and refinement of a result of Xie and Xie (1988). Polyak and Tsypkin comment that the second condition is well known and that the first one is a direct corollary of Newton's test for a polynomial to have only real roots. The original authors express their appreciation for certain points but state that their intention was to point out two conditions for use in stability analysis.<
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