The paper studies the problem of reachability for linear systems in the presence of uncertain input disturbances that may also be interpreted as the action of an adversary in a game-theoretic setting. It emphasizes the differences between reachability under open-loop and closed-loop control. The situation when observations arrive at given isolated instances of time, leads to problems of anticipative (maxmin) or nonanticipative (minmax) piecewise open-loop control with corrections. As the number of corrections tends to infinity, one comes in both cases to a nonanticipative feedback control strategy that ensures reachability under uncertainty and may be found through a solution of the forward Hamilton-JacobiBellman-Isaacs equation. The basic relations are derived through the investigation of superpositions of value functions for appropriate sequential maxmin or minmax problems of control.
Alexander B. Kurzhanski, Pravin Varaiya