  This paper addresses the problem of formation control and tracking a of
desired trajectory by an Euler-Lagrange multi-agent systems. It is inspired by
recent results by Qingkai et al. and adopts an event-triggered control strategy
to reduce the number of communications between agents. For that purpose, to
evaluate its control input, each agent maintains estimators of the states of
the other agents. Communication is triggered when the discrepancy between the
actual state of an agent and the corresponding estimate reaches some threshold.
The impact of additive state perturbations on the formation control is studied.
A condition for the convergence of the multi-agent system to a stable formation
is studied. Simulations show the effectiveness of the proposed approach.
