Controlability and observability of composite systems

This paper studies the controllability and observability of the parallel and the tandem connection of two linear time-invariant differential systems; it uses the Jordan form representation; it does not assume that the eigenvalues of each representation are simple nor that the two sets of the eigenvalues are disjoint. The controllability and observability of the composite representations require only testing the linear independence of some constant vectors. Some sufficient conditions require just the transfer function matrices.