Author: William Bryant
Date: 08:40:57 09/11/99
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On September 11, 1999 at 11:26:45, William Bryant wrote: >On September 11, 1999 at 00:19:40, Robert Hyatt wrote: > >>That seems to be backward. If score > beta, the _current move_ you just >>searched failed high. That move should be stored in the hash table to try it >>first the next time you search this position. The problem we are discussing >>is the _other_ case.. the one where you search all movs and still end up >>with best == alpha, which means all moves were bad... > >Alright, > on re-rereading, let me try this again. > >You completed a ply and found no new alpha (failed-low). >alpha is already greater than a constant MateScore (Mate - some constant). > >You store this in the hash table as follows. > >if (alpha>MateScore) > store the value as MateScore and the flag as hash_Lower to show that this > is the lowest value this position could have. > Because you failed low, there is not best move. > >if (alpha<-MateScore) > storethis normally, with the flag hash_Upper to show that this is the > highest value this position could have. > Again, because you failed low, there is no best move. > >Closer? > Actually, One more try-- it is the extremes on a fail low node that cause problems when abs(alpha) > MateScore so, if (alpha>MateScore) store the value as MateScore and the flag as hash_Lower to show that this is the lowest value this position could have. Because you failed low, there is no best move. if (alpha<-MateScore) store this with a score of -MateScore, with the flag hash_Upper to show that this is the highest value this position could have. Again, because you failed low, there is no best move. Even Closer? William wbryant@ix.netcom.com
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