Author: Klaus Friedel
Date: 13:28:15 01/17/04
Most engines use nullmove to prune the search tree. Before searching the first real move we make a nullmove and search this subtree with depth - R. If this search returns a score above beta we return beta immediately. This kind of pruning is known to be secure in most positions. It will for example fail in Zugzwang positions. But depending on the value of R (most of us use R=2 or R=3) it will fail in other positions. There are two kinds of errors: 1. The null search returns a value < beta where it should return one above. 2. The null search returns a value >= beta where it shouldn't. The first error will only increase nodes to solution. The second is worse. It cuts subtrees that might have changed the search result. Now the question: What are characteristic attributes of posiitions in which the null search is more likely to fail with error 2 (besides zugzwang positions). Regards, Klaus Friedel.
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