In this paper, the formation control of networks of multiple agents is studied via controllability, where the network is under leader-follower structure with some agents taking the leader role and others being followers interconnected via neighbor-based rule. It is shown that the controllability of a multi-agent system is uniquely determined by the topology structure of interconnection graph, and the investigation of which comes down to that for a multi-agent system with the interconnection graph being connected. Based on these observations, two kinds of interconnection graph topologies are characterized, under which the network of multiple agents is uncontrollable, revealing to some extent how the controllability, and accordingly the formation control, are affected by the interconnection topology between agents. Finally, a necessary and sufficient condition in terms of eigenvector is presented. The results also touch upon the selection of leaders and are illustrated by several examples.

Recently, graphical characterization of multiagent controllability has been studied extensively. A major effort in the study is to determine controllability directly from topology structures of communication graphs. In this paper, we proposed the concept of controllability destructive nodes, which indicates that the difficulty in graphical characterization turns out to be the identification of topology structures of controllability destructive nodes. It is shown that each kind of double and triple controllability destructive nodes happens to have a uniform topology structure which can be defined similarly. The definition, however, is verified not to be applicable to the topology structures of quadruple controllability destructive (QCD) nodes. Even so, a design method is proposed to uncover topology structures of QCD nodes for graphs with any size, and a complete graphical characterization is presented for the graphs consisting of five vertices. One advantage of the established complete graphical characterization is that the controllability of any graph with any selection of leaders can be determined directly from the identified/defined destructive topology structures. The results generate several necessary and sufficient graphical conditions for controllability. A key step of arriving at these results is the discovery of a relationship between the topology structure of the controllability destructive nodes and a corresponding eigenvector of the Laplacian matrix.

This note investigates the controllability issues of multi-agent systems, where each node contains generic linear dynamics. First, a neighbor-based control protocol is proposed, under which it is shown that the controllability of a multi-agent system is solely decided by its communication topology structure. We then further consider the effects of communication topology on the controllability from a graph theory point of view by explicitly constructing topologies. The construction exhibits a partition of the designed graph with identified leaders under which the system is shown to be uncontrollable.Index Terms-Controllability, local interactions, leaderfollower structure, multi-agent systems 0018-9286 (c)

The consensus problem for second-order multiagent systems with absolute velocity damping under directed topologies is investigated. In contrast to the existing results, which rely on a sufficiently large common absolute velocity damping gain above a lower bound dependent on global information, this paper focuses on novel algorithms to overcome this limitation. A novel consensus algorithm, where different agents use different absolute velocity damping gains, is first proposed. In the absence of delays, based on a system transformation method, the consensus problem for second-order multiagent systems is converted into that for first-order multiagent systems with the agent number doubled. Necessary and sufficient conditions are then derived under directed topologies by relating the topologies associated with the doubled number of agents and the original team of agents. In the presence of multiple constant delays, based on a further system transformation method, the consensus problem for second-order multiagent systems is converted into the stability problem for corresponding systems. Necessary and sufficient conditions are presented to guarantee consensus under a directed fixed topology. For systems with a uniform constant delay, more concrete necessary and sufficient conditions on how large the delay can be to guarantee consensus is given. Numerical simulations are provided to illustrate the effectiveness of the obtained theoretical results.

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