  In this paper we study the dynamics of a class of bi-agent logistics systems
consisting of two types of agents interacting on an arbitrary complex network.
By approximating the system with simple microscopic models and solving them
analytically, we reveal some universal dynamical features of such logistics
systems, and propose the applications of such features for system
optimisations. Large scale agent-based numerical simulations are also carried
out to explore more realistic and complicated systems, with interesting
emergent behaviours that can be well understood from our analytical studies.
Using the taxi system as a typical logistics system with commuters and empty
taxis as two types of agents, we illustrate two dynamical phases with distinct
behaviours, separated by a phase boundary that can be identified as the optimal
number of taxis for a particular taxi system. We show that these features, and
the tuning of the optimal number of taxis, can be applied to various
situations, including taxi systems allowing real-time dynamical ride-sharing.
Our studies could lead to a theoretical basis for the understanding of a large
class of bi-agent logistics systems, that can be useful for systematic
optimisations via judicious benchmarking of routing and resource allocation
strategies.
