1. BOSE , N. K. , and Zeheb , E.Proc. Institution of Electrical Engineers, Pt G, 1986 , 133 , 187 – 190 .
2. Patel , R. V. , and Toda , M. , 1980 , Quantitative measure of robustness for multivariable systems.Proceedings of the Joint Automatic Control Conference, Paper TP8-A , San Francisco , California