Author: Leen Ammeraal
Date: 09:36:52 02/28/01
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On February 28, 2001 at 07:28:47, Dieter Buerssner wrote: >On February 28, 2001 at 05:56:36, Leen Ammeraal wrote: > >>I am not sure about when to avoid nullmoves. >>I omit it: >>a. when in check >>b. when there are less than 5 pieces (including pawns) on the board > >I think, it is very risky to do nullmoves in pawn endgames, especially when the >position is blocked. > >>c. when the last move was a nullmove > >Vincent has described a method, to allways do exactly two nullmoves in a row. I >do something similar in Yace.´I search the position at even more reduced depth, >than depth-R-1 without doing a nullmove. Only when this gives a fail high, I >allow a nullmove cutoff. Essentially, this is the same than the double nullmove >of Vincent. With this method, Zugzwang situations will be detected eventually. >The drawback is, that you will get less nullmove cutoffs. As seen in various >postings here, i.e. Fritz won't use this more secure approach, and therefor may >fail to see certain short mates. But I have no doubt, that its author is fully >aware of this, and probably knows, that the more risky approach yields in better >results. > >>d. at the root node >>Should I also omit it in some other cases, >>for example, when any hashmove (even with a low draft) was found, > >There are situations, where the hash information indicates, that the null move >will not yield in a cutoff. I.e. when you have an upperbound value in the hash, >that was searched with enoug depth, and the score is smaller beta. > >>or when beta = alpha + 1? > >I don't think, that nullmove should be avoided here. Neither did I, but in Heinz's book, p. 25, I read the following, which made me wonder about null windows: "...null-move pruning generates selective cutoffs at nominal full-width nodes..." Could you (or anyone else, preferably Heinz himself?) please tell me what he means by 'nominal full-width nodes'? By the way, thanks for your response, and my compliments for your wonderful program YACE. Leen
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