  In this paper, we consider the output synchronization problem for a network
of heterogeneous diffusively-coupled nonlinear agents. Specifically, we show
how the (non-identical) agents can be controlled in such a way that their
outputs asymptotically track the output of a prescribed nonlinear exosystem.
The problem is solved in two steps. In the first step, the problem of achieving
consensus among (identical) nonlinear reference generators is addressed. In
this respect, it is shown how the techniques recently developed to solve the
consensus problem among linear agents can be extended to agents modeled by
nonlinear d-dimensional differential equations, under the assumption that the
communication graph is connected. In the second step, the theory of nonlinear
output regulation is applied in a decentralized control mode, to force the
output of each agent of the network to robustly track the (synchronized) output
of a local reference model.
