Author: Uri Blass
Date: 10:06:48 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? Not for me and I think that not for most of the programs. >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. Another mistake The rest should be sorted. If I understand correctly good capture can be the last move if the rest are not sorted in any way. I doubt if you really mean it and I guess that at least that you search captures before no captures also in the first ply. >All I know is that the second move should never be better than the first, that >would be a sign something is wrong. The second move is often better than the first because programs often change their mind. >I guess I can call it a fail low for the >first move (relative to the second move). > >-S. I do not understand what do you call fail low. I call fail low only cases when I find that the first move is bad and I do not know exactly how bad. Cases when the program change it's mind can be described as fail high because I do not know the exact score when I search with window of 1. There are cases when the research does not verify the fail high and in these cases it is a wrong fail high and the program does not change it's mind. Uri
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