Performance limitations in the robust servomechanism problem for discrete time periodic systems (Q1810576)

Using the lifting technique and previous results of the authors, one has here a characterization of the robust servomechanism problem for linear discrete periodic systems. The existence of a solution, the form of the cost and the form of the optimal controller are obtained from the lifted system. The claimed improvement is that the cost contains also a small term depending on the control, but the performance limitations announced in the abstract and the title are expressed only when the small term tends to zero.