Inequality-Based Properties of Detectability and Stabilizability of Linear Time-Varying Systems in Discrete Time

Well-known properties of uniform detectability and uniform stabilizability are sharpened in terms of Lyapunov and Riccati inequalities for discrete-time linear time-varying systems. In particular, it is shown that the stabilizing output injection law can be taken to depend solely on a finite path of past and present system coefficients and the stabilizing state feedback law solely on a finite-path of present and future coefficients. These results are applied to time-varying systems where the system coefficients vary among a finite set, and lead to precise and computable convex conditions for the stability and dynamic-output-feedback stabilizability of such systems.