M. C. Tsai E. J. M. Geddes Ian Postlethwaite Pole-zero cancellations and closed-loop properties of an H∞ mixed sensitivity design problem. 519-530 1992 28 Autom. 3 https://doi.org/10.1016/0005-1098(92)90176-G db/journals/automatica/automatica28.html#TsaiGP92