  A basic result in synchronization of linear systems via output coupling is
presented. For identical discrete-time linear systems that are detectable from
their outputs and neutrally stable, it is shown that a linear output feedback
law exists under which the coupled systems globally asymptotically synchronize
for all fixed connected (asymmetrical) network topologies. An algorithm is
provided to compute such feedback law based on individual system parameters. A
dual problem is also presented and solved.
