This paper describes the design and development of two w0rld-class Lines of Action game-playing programs: YL, a three time Computer Olympiad gold-medal winner, and MaNA, which has dorninated international e-mail correspondence play. The underlying design philosophy of the two programs is very different: the former emphasizes fast and efficient search, whereas the latter focuses on a sophisticated but relatively slow evaluation of each board position. In addition to providing a technical description of each program, we explore some long-standing questions on the trade-offs between search and knowledge. These experimental results confirm the conclusions made by earlier researchers in the domain of chess, thus showing that the trends are not game-specific. In particular, we see dirninishing retums with additional search depth, and observe that the knowledge level of a program has a significant impact on the results of such experiments.Keywords: Lines of Action, search, knowledge
IntroductionOne of the most important considerations when designing a strategic gameplaying program is the trade-off between know ledge and search.To decide on the best move continuation, programs typicallx perfonn a lookahead search, evaluate the positions at the leaves of the search tree, and then propagate those values back to the root using the minimax principle. A program that uses a sophisticated but time-consuming board evaluation can more accurately determine the merit of each game-state visited, at the cost of sacrificing some of the look-ahead depth. Conversely, a program that uses a faster but less sophisticated board evaluation method can perform a deeper search, improving its short-term tactica! ability. There is also compensation toward better knowledge, in that each additionallevel of search provides a more refined approximation of the value of each preceding position.The trade-off between knowledge vs. search has spurred a considerable amount of research interest in the past, mainly for the game of chess (Schaeffer, 1986;Berliner et al
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