Author: Sune Fischer
Date: 10:33:52 08/02/03
Go up one level in this thread
On August 02, 2003 at 12:48:05, Omid David Tabibi wrote: >On August 02, 2003 at 12:15:18, Sune Fischer wrote: > >>On August 02, 2003 at 11:12:29, Tony Werten wrote: >> >>>>To summarize, a score can be considered "exact" only if it has been achieved >>>>independent of alpha and beta bounds. This is the case only if we are at a leaf >>>>node with full evaluation, or other node with alpha < value < beta. >>> >>>Or when a checkmate score is returned or a drawscore or .... >> >>This is not true. >> >>Consider a case where beta<=0, the first move you search bring back a draw score >>(say, forced repetition). >>Now you fail high without checking the rest, but you could have had a mating >>move or another winning line you didn't search. So it will just be a lower >>bound. > >Again, the decision was based on the bounds, so it was by no means an exact >score. When you encounter a threefold repetition, you may store it as exact >score in the current node, Unless you've searched all the moves at that node, you can't be sure it is an exact score, because you might find an even better move among the remaining ones. The only exception I can think of would be a mate in 1, you can store that as exact :) >but when you return 0 to the father, you treat it >there just as a normal score, so if it is not between alpha and beta, you cannot >store it as exact. True. >(Looking at my code I see that I don't store repetition draws in the hash table >at all, I have commented it out, but I'm not sure why :) Well it makes some sense, since the hash shouldn't be used to store path dependent scores. It doesn't solve the problem though. -S.
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