Robustnessofcontrolsystemstodisturbancesanduncertaintieshasalwaysbeenthecentralissueinfeedbackcontrol.Feedbackwouldnotbeneededformostcontrolsystemsiftherewerenodisturbancesanduncertainties.Developingmultivariablerobustcontrolmethodshasbeenthefocalpointinthelasttwodecadesinthecontrol