Author: Bas Hamstra
Date: 05:57:41 09/17/99
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On September 16, 1999 at 13:50:18, Alessandro Damiani wrote: >On September 16, 1999 at 12:46:20, Peter Fendrich wrote: > >>On September 16, 1999 at 05:18:42, Bas Hamstra wrote: >> >>- snip - >> >>>History: >>> >>>(I never used it) >>> >>>A table of counters, used for movesorting. You use a table History[From][To] to >>>keep track of the number of beta cutoffs for each move [From][To]. And use that >>>to improve the probability of a cutoff (as you do with killers). If you already >>>use more than 1 killer I have the impression History doesn't give much extra. >>> >>I don't agree with you here. My implementation of killer table only has effect >>on local parts of the tree. For each new path the killer moves are cleared. The >>history table is covering all of the tree and really improves move ordering in >>some nodes. Normally there is no big overlap betwee the two. >>//Peter > >I agree with you, Peter. That is the idea of history heuristic. It should not >only be used when a cut-off occurs, but always when there is a best move. > >And since everybody knows that there is no best move at a fail-low, the history >table should only be updated if > > best>alpha > >where best is the score of the best move. > >Alessandro How do you update killers? I store a killer when anything but the first move (not being a capture) is > Alpha. That seems to work better than storing only when >= Beta. It works less well when: a: I also include first moves b: I update killers only when move >= beta in stead of > Alpha. Regards, Bas Hamstra.
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