Author: Peter Fendrich
Date: 10:16:03 09/28/02
Go up one level in this thread
On September 28, 2002 at 12:56:16, Sune Fischer wrote: >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? Try it! I use a window about 1 pawn value wide. In that case you can fail low and have to re-search. I once tried to continue with the second hoping it would be better that the first. After that I took move 1,3,4 etc. > >I do search the best move from the previous depth first, the rest are not sorted in any way. On way to sort is to use the node count. High node counts indicates that "something is going on" and gives a fairly good sequence when the first move is not good any more. >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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