I. Introduction
Multi-agent navigation algorithms are widely used for motion planning among static and dynamic obstacles [1], for autonomous localization [2], and in the simulation of animated characters or human crowds in games and virtual worlds [3]. A key issue in these applications is collision-free path planning: given a set of agents in a static or a dynamic environment, each with its own initial and goal positions, computing collision-free trajectories for each agent towards its goal. In some scenarios, there are additional constraints imposed on the trajectories corresponding to dynamics, biomechanics, or human-like behaviors.