Author: Dieter Buerssner
Date: 04:28:47 02/28/01
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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. I also avoid nullmove, when alpha is a mate score. Regards, Dieter
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