Contributions to a hierarchical theory of systems

Linear time-invariant systems are considered as aggregates of subsystems, which again may be composed of subsystems at a lower level, and so on. No special structure is supposed for the system, apart from that imposed by the method of interconnection. Some basic results are established, and applications made to analogue computers and to electrical networks. In particular it is shown that when a proper n-port impedance matrix can be realized (without ideal transformers) only by using more reactive elements than the McMillan degree would suggest, still the realization may have least order.