Hi. I would appreciate if some one could help me with my question. But first some background: There is a classical problem of inverted pendulum under control. Pendulum can be put to UNSTABLE equlibrium and (if no control applied) it can put itself to STABLE equlibrium. So system under control goes from MAXIMUM potential Energy to its MINIMUM potential energy. So keeping system in ONE state forever is the goal of the problem. ///////////////////////////////////////////////////////////////////////// The QUESTION: Are there models\systems (under control and without one) which are sole purpose to continuously go from Stable to Unstable equlibriums i.e. continiously switch states (and do so in optimal way) and not trying to keep just one of them forever. thanks.