A new upper bound for the skewed structured singular value

The structured singular value (s.s.v) mu enables the study of robust stabil ity and performance of a controller in the presence of real parametric unce rtainties and complex uncertainties corresponding to neglected dynamics. In spite of the NP-hard characteristic of the problem, it is now possible to compute an interval for the s.s.v. mu using polynomial-time algorithms. The skewed s.s.v. nu was introduced by Fan and Tits(1) in the context of robus t performance analysis. The primary aim of this paper is to propose a new m ixed nu upper bound, which is applicable to problems with a special, but pr actically important, structure. We then illustrate through a realistic miss ile example that certain problems naturally require the nu tool rather than the mu tool. Copyright (C) 1999 John Wiley & Sons, Ltd.