Comments on "Controllability and observability of composite systems"

In a recent paper, a sufficient condition for controllability (observability) of two systems connected in tandem having the most general Jordan form of representation was given. In this correspondence, a counterexample to this sufficient condition is given and further assumptions under which this condition is necessary as well as sufficient are indicated.

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[2]  S. Panda Controllability of discrete composite systems , 1970 .