Digital systems
Oscillatory systems

Higher order systems can have also a non-monotonic transient response. Some kind of systems has typical oscillatory response. The essence of this behavior lies in mutual interchange of energy between different forms (accumulators). E.g. in case of suspended pendulum, a potential energy is transformed to a kinetic energy, and vice versa; in case of torsion pendulum, energy of elastic deformation is transformed to a kinetic energy, and vice versa. The oscillatory characteristic can be found in mechanic systems, where an inertia (mass or momentum), springiness (spring or other reversible deformation) and a damping. Commonly, the goal of control system is to increase the damping (e.g. active damping of carriage or driver's seat, crane motion optimization with respect to cancel oscillations). Electric circuits, composed of inductors, capacitors and resistors are also susceptible to oscillation. Large water areas are usually also oscillatory. Oscillation, even unstable, is often caused by a feedback in complex systems.

Series connection of subsystems can be composed not only of static systems, but of the astatic or a combination of static and astatic as well.

Fig. 8.12: Electric circuit of RLC type