“…Although early papers were based on the restrictive assumption that each input-output pair had the same time delay, more recently developed design methods can accommodate arbitrary time delays for each pair (Morris et al, 1981(Morris et al, , 1982Tanttu and Koivo, 1983;Chien et al, 1984aChien et al, , 1985aDugard et al, 1984). A few design methods permit different numbers of inputs and outputs ( Wong and Bayoumi, 1981;Favier and Hassani, 1982;Grimble et al, 1982;Toivonen, 1983b) or a different sampling rate for each output variable (Morris et al, 1981(Morris et al, , 1982Chien et al, 1983;Costin and Buchner, 1983). Some multivariable self-tuners are applicable to plants that are either open-loop and unstable or nonminimum-phase (McDermott and Mellichamp, 1983;Grimble and Moir, 1983).…”