Henry W. Davis

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In high-performance A* searching to solve satisfici n g prob lems, there is a c r i t i ca l need to design heur is t ics which cause low t ime-complex i ty . In order for humans or machines to do this effectively, there mus t be an unders tand ing of the domainindependent properties that such heurist ics have. We snow that , contrary to common belief,(More)
Three admissible bidirectional search algorithms have been described in the literature: A Cartesian product approach due to Doran, Pohl's BHPA, and Champeaux and Sint's BHFFA2. This paper describes an algorithm, GP, which contains the latter two and others. New admissibility results are obtained. A first order analysis is made comparing the run times of(More)
Two models of heuristics have been suggested in previous studies of A* tree-searching. The models are used to determine what mathematical properties heuristics must have if A* is to have polynomial, versus exponential, average asymptotic time complexity. In the EC model polynomial A* complexity is associated with logarithmic heuristic error. In the NC model(More)
Previous studies of A* tree-searching have modeled heuristics as random variables. The average number of nodes expanded is expressed asymptotically in terms of distance to goal. The conclusion reached is that A* complexity is an exponential function of heuristic error: Polynomial error implies exponential complexity and logarithmic accuracy is required for(More)