Comments on "Strictly positive real transfer functions revisited

In the original paper, by R. Lozano-Leal and S. Joshi (lEEE Trans. Automat. Contr., vol. 35, no. 11, p. 1243-5, 1990), the distinction between weak and strong strictly positive real (SPR) functions was addressed, and the feedback interconnection of a weak SPR system and a passive one was shown to be stable. The purpose of this note is to show that the proof of this lemma is actually incorrect.<
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