  We present a new algorithm to simulate dynamic group behaviors for
interactive multi-agent crowd simulation. Our approach is general and makes no
assumption about the environment, shape, or size of the groups. We use the
least effort principle to perform coherent group navigation and present
efficient inter-group and intra-group maintenance techniques. We extend the
reciprocal collision avoidance scheme to perform agent-group and group-group
collision avoidance that can generate collision-free as well as coherent and
trajectories. The additional overhead of dynamic group simulation is relatively
small. We highlight its interactive performance on complex scenarios with
hundreds of agents and compare the trajectory behaviors with real-world videos.
