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Subject: Re: I hate null moves

Author: Ed Schröder

Date: 01:10:29 01/30/04

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On January 30, 2004 at 03:40:57, Tord Romstad wrote:

>Recursive null move pruning is an effective way to speed up the search of
>a chess engine, but I really detest its unfortunate side effects.  Most of all
>i hate its tendency to cause search inconsistencies, and that it tends to prune
>away strong lines where a piece must traverse a long and complicated path in
>order to reach a good square.  I try to cure the second problem by using a
>dynamic reduction factor, and I also plan to experiment with Markoff's idea
>of trajectories to see if that can help to reduce the problem further.  I have
>no idea what to do with the search inconsistencies.
>
>Most of all, I would like to throw away null move pruning (at least in its
>traditional form) completely.  Unfortunately my attempts to get rid of it have
>so far been very unsuccessful.  It simply slows down my engine too much, and
>the other pruning I do is not enough to compensate.  I really need some
>effective replacement for recursive null move pruning.
>
>Are there any known algorithms which are close to null move pruning in terms
>of efficiency?  It is clear that such techniques exist, for instance whatever
>Junior and Tiger do appears to be at least as effective.  But I cannot recall
>having seen any really interesting ideas discussed in public.
>
>Tord


Tord,

I am sure you have read Rebel's approach -> static selective search as a base
and controlled by nullmove during the first x plies catching the errors of the
static evaluation.

My best,

Ed



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