An Algorithm Better than AO*?

Blai Bonet, Hector Geffner

Recently there has been a renewed interest in AO* as planning problems involving uncertainty and feedback can be naturally formulated as AND/OR graphs. In this work, we carry out what is probably the first detailed empirical evaluation of AO* in relation to other AND/OR search algorithms. We compare AO* with two other methods: the well-known Value Iteration (VI) algorithm, and a new algorithm, Learning in Depth-First Search (LDFS). We consider instances from four domains, use three different heuristic functions, and focus on the optimization of cost in the worst case (Max AND/OR graphs). Roughly we find that while AO* does better than VI in the presence of informed heuristics, VI does better than recent extensions of AO* in the presence of cycles in the AND/OR graph. At the same time, LDFS and its variant Bounded LDFS, which can be regarded as extensions of IDA*, are almost never slower than either AO* or VI, and in many cases, are orders-of-magnitude faster.

Content Area: 18.Search

Subjects: 15. Problem Solving; 15.7 Search

Submitted: May 10, 2005


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