Output feedback stabilization of uncertain dynamical systems

Given an uncertain dynamical system with a linear nominal part, matched uncertainties, and a measured output, a sufficient condition is given for the existence of an output feedback stabilizing controller. For the general multiinput multioutput case, checking the sufficient condition involves the selection of a matrix . For the special class of single input single output systems, is a positive or negative scalar and it is shown that if the nominal system transfer function is strictly positive real, then an output feedback stabilizing controller does indeed exist.