“…A dynamic system, or process, is defmed by input variables Ul(t), ... , up (t), which are used to influence the system, and output variables Yl(t), ... , yq(t), whose dynamic behaviour is of major interest [Follinger, Franke, 1982]. In order to obtain a system of normal differential equations representing the relationship between input and output variables, intermediate variables, which are called state variables x,(t), ... , xn(t), are used.…”