Robustness under bounded uncertainty with phase information

The authors consider uncertain linear systems where the uncertainties, in addition to being bounded, also satisfy constraints on their phase. In this context, the authors define the "phase-sensitive structured singular value" (PS-SSV) of a matrix and show that sufficient (and sometimes necessary) conditions for stability of such uncertain linear systems can be rewritten as conditions involving PS-SSV. They then derive upper bounds for PS-SSV, computable via convex optimization. They extend these results to the case where the uncertainties are structured (diagonal or block-diagonal, for instance).