Two is Not Always Better than One: Experiences in Real-Time Bidirectional Search

This paper investigates real-time bidirectional search (RTBS) algorithms, where two problem solving agents, starting from the initial and goal states, physically move toward each other. To evaluate the RTBS performance, two kinds of algorithms, centralized RTBS and decoupled RTBS, are proposed and are compared to real-time unidirectional search (RTUS). Experiments on mazes and n-puzzles show that (1) in clear situations decoupled RTBS performs better, while in uncertain situations, centralized RTBS becomes more e cient, and that (2) RTBS is more e cient than RTUS for 15and 24-puzzles but not for randomly generated mazes. It will be shown that the selection of the multi-agent organization is the selection of the problem space, which determines the baseline of the organizational e ciency; once a di cult problem space is selected, the local coordination among problem solvers hardly overcomes the de cit.