  This paper proposes a label-free controller for a second-order multi-agent
system to cooperatively fence a moving target of variational velocity into a
convex hull formed by the agents whereas maintaining a rigid formation.
Therein, no label is predetermined for a specified agent. To attain a rigid
formation with guaranteed collision avoidance, each controller consists of two
terms: a dynamic regulator with an internal model to drive agents towards the
moving target merely by position information feedback, and a repulsive force
between each pair of adjacent agents. Significantly, sufficient conditions are
derived to guarantee the asymptotic stability of the closed-loop systems
governed by the proposed fencing controller. Rigorous analysis is provided to
eliminate the strong nonlinear couplings induced by the label-free property.
Finally, the effectiveness of the controller is substantiated by numerical
simulations.
