Author: Will Singleton
Date: 23:21:58 04/05/00
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On April 06, 2000 at 00:45:28, Nobuhiro Yoshimura wrote: >On April 05, 2000 at 20:57:30, Robert Hyatt wrote: > >>On April 05, 2000 at 20:54:52, Nobuhiro Yoshimura wrote: >> >>> I am writing a Japanese Chess program using PVS with iterative deeping and >>>hash tables. I often get a fail-low at the root node at the end stage of >>>the game. I would like to know how offten do you get fail-lows in >>>searching the chess game tree and also what kind of bugs are possible to >>>cause many fai-lows. >> >> >>I don't quite understand why you think it is a bug. IE sometimes when you >>go a ply deeper, you discover some threat your opponent has that you simply >>can't defend against, and the score drops. It is not abnormal... > >I just thought that since PVS is a good searching algorithm and is >being used by many chess programmers that it would not produce >many fail-lows that are very bad for search efficincy. I'm not sure if you understand this or not, but a fail-low or -high is simply a returned score that's outside your current search window. The benefit from using a narrow search window outwieghs the cost of researching after the failure. Having said that, let me say that I use PVS, but I don't use a narrow window at the root. I always use +- inf, so no fails or researching is necessary. My testing shows that PVS doesn't benefit that much, if at all, from the narrow window. Will
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