Comments on “A Note on Spectral Conditions for Positive Realness of Single-Input-Single-Output Systems With Strictly Proper Transfer Functions”

The necessary and sufficient conditions for (strict) positive realness of strictly proper transfer functions are derived in the above-mentioned paper

. Presenting a counter-example, we show that there are inconsistencies between definitions stated in
Section II
and main results proved in section III of

. Also, the required corrections in the main results of

are presented. Note however that the results in

are correct for the definition of SPR in the Circuit Theory sense.