Author: Russell Reagan
Date: 20:27:03 01/28/04
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On January 28, 2004 at 22:50:05, Robert Hyatt wrote: >Bruce's case is a pathological problem that will happen. But it is caused by an >extreme happening. In a normal search this won't/can't happen (assuming you are >not using null-move). But in reality it can. However, 99.9% of the time, >re-searching with beta,+infinity after a fail high on alpha,beta will produce a >score as expected... Okay, let me see if I understand what's going on. In your newsgroup post, you were speaking from a theoretical point of view, while Bruce was speaking from a practical view where search instability has already crept in (via null-move, or whatever). As long as you're doing pure alpha-beta with aspiration search, it is safe to assume that the real score of a failed aspiration search will be (-infinity, alpha+1) for a fail low, and (beta-1, +infinity) for a fail high. This kind of search instability problem is introduced by the same position being handled differently at different parts of the tree due to their different paths (ex. use of a transposition table, null-move or any forward pruning done based upon alpha or beta, 3-fold-repetition, 50 move rule, etc.). Is that all correct?
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