A note on "An example in decentralized control systems"

In this correspondence we discuss an example given recently by Wang in the above paper of a system which cannot be stabilized by decentralized state feedback, although the overall system and the local ones are controllable. The reasons for which the above mentioned system cannot be decentrally controlled are given explicitly in terms of the graph of the system, and a suggestion-formulated as a conjecture-is presented on the conditions an interconnected system should satisfy to be controlled by decentralized state feedback.