On the decentralized control of interconnected dynamical systems

It is shown that rise fixed modes of an interconnected dynamical system under decentralized control are precisely the uncontrollable and unobservable states of the individual system components. As such, the system can be stabilized by decentralized controllers if and only if its individual system components can be stabilized. Moreover, these conditions are shown to be equivalent to the conditions for stabilizing the system using a global controller.