“…1983), while other work has aimed to increase understanding of the problems (Astrom 1983(Astrom , 1984 Chen and Cook 1984, Rohrs 1985, Kidd 1985 Ioannou and Kokotovic 1984 a). Robustness enhancement schemes have also been proposed (Ioannou andKokotovic 1984 a, b, Ioannou 1985, Riedle and Kokotovic 1985, Chen 1987, Mufti 1989). …”