On stability radii of infinite–dimensional time–varying discrete––time systems

This note introduces a stability radius for discrete–time linear time–varying systems on Banach spaces under structured time–varying perturbations of multiple–output feedback type. Additive perturbations are considered which can be represented as a series of infinitely many perturbation terms. We derive counterparts to some results established for time–varying differentiable systems in [5, 7] and apply the results to periodic systems.