Author: Ernst A. Heinz
Date: 09:15:22 08/23/00
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Hi Dieter, >Both use zero window searches with -alpha-1, -alpha for the recursive call. >If the score returned from the recursive call is > alpha and < beta, Negascout >will research with -beta, -score while PVS will research with -beta, -alpha. There might be some confusion in the literature, but I am quite sure that the distinction you describe relates to the so-called "fail-hard" and "fail-soft" versions of alpha-beta search. The fail-soft variant "raises" the upper bound of recursive search calls to "-max(alpha, score)" and the upper bound of PVS researches to "-score + 1". Chapter 0 of my book "Scalable Search in Computer Chess" provides more details about the topic (for more information on the book see http://supertech.lcs.mit.edu/~heinz/node1.html). =Ernst=
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