Author: Dieter Buerssner
Date: 11:07:43 08/13/01
Go up one level in this thread
On August 13, 2001 at 00:01:35, Robert Hyatt wrote: >On August 12, 2001 at 23:49:35, Pham Minh Tri wrote: > >>How about the UPPER? Should we choose the move has score nearest alpha (the >>highest score or the first of highest ones)? Perhaps store something is better >>than nothing. >> > >Nope. Something is not better than nothing here. In a LOWER position, every >move was refuted by the next ply. I am not sure, if I understand LOWER here. Don't you mean an upper bound position: One for which you have a score, that is an upper bound (so the score is this or lower). Or in other words, the search failed low for this position. >You know nothing about which move is best, >only that every move is bad. Better to let normal move ordering take over >here rather than taking a guess. Note that even picking the move closest to >alpha is worthless... because the scores are not produced so that this will >work. You won't know how bad each move is, just that each one is bad... > >Store a zero, and try normal ordering ideas like good captures, etc... I have found a small reduction of tree sizes, when keeping track of and storing upper bound moves in the hash table. I don't necessarily try them first in the search, but just shuffle them a bit up in the move ordering. The difference to Crafty might be, that I almost exclusively use fail soft alpha-beta. So, instead of all moves having the same score, the scores can (and will) vary in the case of fail low. For example, for any move, besides one there may be a mate score. Regards, Dieter
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