Author: Sune Fischer
Date: 09:56:16 09/28/02
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On September 28, 2002 at 12:20:00, Robert Hyatt wrote: >On September 28, 2002 at 11:38:19, Sune Fischer wrote: > >>Carlos Pagador just sent me a game where frenzee made a clear blunder move. >> >>It wasn't a bug in the search, but in the time management. >>What happened was that the pv move failed-low at the root (I think that's what >>it's called?), it was a mate in 3 so it had to be avoided. >> >>The searched continued and the second move searched happened to be a very bad >>queen "sacrifice"! >> >>Unfortunately time was up before it could search the third move, so it played >>this losing queen move. >> >>It could have been worse actually, if it hadn't searched the second move either >>it would have gone straight into the mate, not suspecting the move was bad at >>all. >> >>I wonder how many buggy moves are made because of these fail-lows, I never >>thought about this at all, but of course the actual move being returned could be >>almost random when this happens. I reckon this is common knowledge, I just don't >>remember having seen it explained anywhere? > > >It is easy to fix. If you fail low on the _first_ root move, then re-search >it right then to get a score. Now you know how bad things are and how much >time you are willing to invest in order to find a better move... Okay, chess lingo question: how can I fail low on the first root move, the alpha value is -inf? I don't do aspiration search or anything at the first move, should I? I do search the best move from the previous depth first, the rest are not sorted in any way. All I know is that the second move should never be better than the first, that would be a sign something is wrong. I guess I can call it a fail low for the first move (relative to the second move). -S.
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