Author: Tord Romstad
Date: 00:40:57 01/30/04
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
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