Computing the distance to an uncontrollable system

Algorithms for computing the distance from a particular controllable system to the closest uncontrollable system are presented. An interpretation of the problem is suggested, and some results from earlier research are unified. The interpretation suggested and the associated theoretical results lead to an efficient iterative algorithm for computing the closest system. Algorithms are presented for both the real and the complex perturbation problem, when the system under investigation is real or complex. Real perturbations occurring to complex systems are considered