  This paper presents a new approach to distributed nonlinear control for
formation acquisition and maintenance, inspired by recent results on cyclic
topologies and based on tools from contraction theory. First, simple nonlinear
control laws are derived to achieve global exponential convergence to basic
symmetric formations. Next, convergence to more complex structures is obtained
using control laws based on the idea of convergence primitives, linear
combinations of basic control elements. All control laws use only local
information and communication to achieve a desired global behavior.
