Comments on “Dissipative analysis and control of state-space symmetric systems” [Automatica 45 (2009) 1574–1579]

We show that some results presented by Meisami-Azad, Mohammadpour, and Grigoriadis [Meisami-Azad, M., Mohammadpour, J. & Grigoriadis, K. M. (2009). Dissipative analysis and control of state-space symmetric systems. Automatica, 45, 1574–1579] are erroneous. First, we present a counterexample contradicting the necessary and sufficient condition of Lemma 5. Then, we point out that Lemma 4, which is a key instrumental lemma in the proof of Theorem 6, is also erroneous and we propose a new lemma that corrects and completes the proof of Theorem 6. Finally, we show that H ∞ norm formulations claimed by Theorems 6, 7 and 8 are inaccurate which is also sustained by previously published results as well as numerical examples taken from the commented paper.