Necessary and sufficient conditions for strictly positive real matrices

In this paper we present some useful properties of strictly positive real transfer matrices for both continuous and discrete-time linear time-invariant systems in the frequency and state space domains. Some of these properties follow from known results and are presented for the sake of completeness. The new results obtained are mainly for discrete-time systems and include the discretetime version of the Lefschetz-Kalman-Yakubovich lemma for transfer matrices.