The efficiency of the alpha-beta search on trees with branch-dependent terminal node scores

摘要

An analysis of the efficiency of the alpha-beta algorithm is carried out based on a probabilistic model in which terminal node scores depend on random branch values. Explicit expressions are derived for the expected number of terminal nodes scored for the cases of uniform trees of fanout N and of depths 2 and 3. For trees of depth 2, the expected number is of order O(NHN); for trees of depth 3, the expected number is of order O(N2). An upper bound on the expected number of terminal nodes scored for trees of depth 4 is shown to be no greater than O(N2HN2) and no less than O(N2).