Wilkie-Perkins low-order sensitivity model revisited

The minimality of the Wilkie-Perkins low-order sensitivity model [1] for multi-input systems is reexamined. An example is offered to provide insight into the optimality discussion of Guardabassi et al. [2]. Then it is indicated that generation of sensitivity functions of arbitrary multi-input systems requires at most
m . n
integrators in addition to the system model.