On the optimality of the Wilkie-Perkins low-order sensitivity model

Some comments on the low-order sensitivity model proposed by Wilkie and Perkins are presented. The structural controllability of this model and the analysis of its observability properties allow one to conclude that the model is optimum in the sense that no lower order sensitivity model exists that can generate all the state sensitivity functions for the class of systems for which the theory developed in Wilkie and Perkins holds.