“…The realization problem, i. e., transforming a set of higher order differential input-output (i/o) equations into a set of first order differential equations, called state equations, has been studied extensively for nonlinear control systems, both in continuous-and discretetime [4,5,8,9,13,18,19,20]. The reason is simple -most of the control theory is developed for systems described by the state equations, although system identification mostly yields the set of i/o equations.…”