Distance of a Controllable System from the Nearest Uncontrollable One
In several control systems applications, it is important to know how "distant" is the given nominal controllable system from an uncontrollable one. In this note we obtain a simple characterization of the measure of the distance and based on the characterization, obtain the bounds on the perturbations in the state and input matrices that will make a controllable system uncontrollable
Chapter, 1989