WHY DO STABILIZING CONTROLLERS STABILIZE

An alternative notion of a stabilizing controller is presented. Being defined in terms of the trajectories of plant and controller, it is we ll suited for situations in which the controller's action is an interc onnecting one. In the second part of the paper, a parametrization is g iven of the kernel representations of all controllers that give rise t o an a priori specified closed-loop behavior. As a special case, the p arametrization yields all stabilizing controllers. Unlike the Youla pa rametrization, it also includes the so-called singular stabilizing con trollers.