Comments on "Zeros of discretized continuous systems expressed in the Euler operator: an asymptotic analysis"

In the original paper by Tesfaye and Tomizuka (ibid., vol.40, p.743-7, 1995), an asymptotic analysis was used to address the zero structure of discretized continuous-time systems expressed in the Euler (or forward difference) operator. The method was developed for application to multivariable control systems. The authors state that the analysis is flawed, so that a theorem is true as stated only when the continuous time relative degree is equal to two. They indicate how the analysis may be rectified. Tesfaye and Tomizuka acknowledge the error and the correctness of the result in this paper.