  This paper considers the controllability problem for multi-agent systems. In
particular, the structural controllability of multi-agent systems under
switching topologies is investigated. The structural controllability of
multi-agent systems is a generalization of the traditional controllability
concept for dynamical systems, and purely based on the communication topologies
among agents. The main contributions of the paper are graph-theoretic
characterizations of the structural controllability for multi-agent systems. It
turns out that the multi-agent system with switching topology is structurally
controllable if and only if the union graph G of the underlying communication
topologies is connected (single leader) or leader-follower connected
(multi-leader). Finally, the paper concludes with several illustrative examples
and discussions of the results and future work.
