Doyle, John: 'Analysis of feedback systems with structured uncertainties', IEE Proceedings D (Control Theory and Applications), 1982, 129, (6), p. 242-250, DOI: 10.1049/ip-d.1982.0053
IET Digital Library, https://digital-library.theiet.org/;jsessionid=6agbhf6n3ei8k.x-iet-live-01content/journals/10.1049/ip-d.1982.0053