Is Best First Search Really Best?

Of the many minimax algorithms, SSS* consistently searches the smallest game trees. Its success can be attributed to the accumulation and use of information acquired while traversing the tree, allowing a best first search strategy. The main disadvantage of SSS* is its excessive storage requirements. This paper describes a class of search algorithms which, though based on the popular alpha-beta algorithm, also acquire and use information to guide their search. They retain their directional nature yet are as good as SSS*, even while searching random trees. Further, while some of these new algorithms also require substantial storage, they are more flexible and can be programmed to use only the space available, at the cost of some degradation in performance. Acknowledgement Financial support from Natural Sciences and Engineering Research Council Grant A7902 made it possible to complete the experimental work described in this report. [Re-created from files dated 2 November 1985 in /cshome/tony/Reports/TR85.16]