Robustness of model reference adaptive controllers: input-output properties

A description is given of a general input-output approach that can be used in the analysis and design of adaptive control systems. The effectiveness of this approach is demonstrated in an application to the model reference adaptive control problem. A sufficient condition for the closed-loop stability is developed. It is based on quantities that can be calculated in a straightforward procedure and allows the study of the effects that the design parameters have on the robustness of the adaptive controller. The results indicate a direction toward a unified, systematic, and quantitative theory of adaptive control