This paper investigates an event-triggered control method for a class of nonlinear multi-agent systems, in which a group of followers surround a group of leaders. Dynamics of leaders and followers are assumed to be heterogeneous and to have unknown parameters. To deal with this problem, some adaptive laws and also controllers including event-triggered estimator of leaders' geometric center are proposed. In order to reduce some dispensable data exchange among the follower agents and save the limited communication resources, event-triggered control protocols are used to attain better performance of resources. The proposed control scheme guarantees that all the closed loop signals are globally bounded and surrounding error converges toward a compact set, exponentially. Moreover, Zeno behavior is also excluded under certain conditions. Eventually, numerical simulations are provided to verify theoretical results and demonstrate that the triggering laws cause decrement of the number of controller updates and inter-agent communications.
