The paper considers the synchronisation of dynamical subsystems by interactions. Asymptotic synchronisation means that all subsystem outputs asymptotically follow the same trajectory. Literature has considered this problem mainly for linear or nonlinear subsystems with diffusive couplings, which appear as physical couplings among the subsystems or as digital couplings among the local subsystem controllers.
A basic assumption requires the subsystems to have identical dynamics. After reviewing the main results for the synchronisation of linear subsystems, the presentation investigates the robustness of synchronised systems with respect to deviations of the subsystems or the couplings from the assumptions mentioned above.
It shows that for oscillator networks even infinitesimally small changes of the agent parameters make the overall system to become asymptotically stable and, hence, not synchronisable with respect to a non-trivial synchronous trajectory. An investigation of this phenomenon shows why the property of synchrony is so sensitive with respect to the subsystem parameters. Consequently, the synchronisation theory of linear multi-agent systems is not applicable because no-one can produce identical agents. Research on synchronised systems has to be directed to a larger class of systems, for example, to affine subsystems like Kuramoto oscillators or to more general nonlinear subsystems like limit-cycle oscillators.