Author: Robert Hyatt
Date: 18:40:43 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? Most use an aspiration search window centered around the score from the prior iteration. If you use -inf, then remember the score from the _last_ iteration. If the score for the first move at this iteration is much lower, then raise your time allowance... >I don't do aspiration search or anything at the first move, should I? Definitely. It speeds things up and is trivial to do, just use last-X,last+X where last is score from previous iteration, and X is some number you like, such as .25 pawns or whatever works best for you... > >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.
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.