Author: Robert Hyatt
Date: 06:56:28 03/17/03
Go up one level in this thread
On March 17, 2003 at 01:14:38, Ralph Patriquin wrote: >On March 16, 2003 at 18:54:18, Robert Hyatt wrote: > >>On March 16, 2003 at 18:32:01, Ralph Patriquin wrote: >> >>>Bob, could you explain what asymmetric evaluation is vs symmetric evaluation, >>>and pro and con for both? Why is it used? Does it impact the end user in what he >>>sees for a numeric score from the computer? Also, I seem to remember some config >>>file setting for Crafty having to do with asymmetric eval, is this the same >>>thing you're talking about here? >>> >>>Thanks, >>> >>>Ralph >> >> >>Asymmetric evaluation is an evaluation that not the same when computed for >>black and white. >> >>One example is blocked pawn positions. Most believe a computer is bad in >>these positions and that such positions make it easier for the human to sneak >>into a drawn position. The solution is to have the program dislike such >>positions so that it won't get into them. Of course, avoiding blocked positions >>all the time is not a good idea, so it needs to be somehow controlled so that >>a program that thinks it is in a bad position might block things to avoid >>opening up a bad position into a much worse position. >> >>It's a matter of taste. Without it, many programs will make ugly looking moves >>such as d4 d5 c4 e6 c5, which starts things toward a blocked queen-side. I >>won't say it is a "cure-all" but it can (if used carefully) help. >> >>Another case is king safety. Programs are bad about understanding an open >>king-side until they see the roof falling in. The fix is to ramp up king safety >>scores, so that it won't try to win a pawn by letting its kingside get wrecked. >>But then it may well offer pawns to wreck the opponent's king-side when it is >>not sound, and lose. Asymmetric king safety will let it avoid wrecking its own >>kingside, while not unsoundly offering material or positional gambits to open >>the opponent's king... > >OK, if I understand this correctly, Crafty will value some feature of the >position (like King safety) higher for itself than its opponent for reasons of >avoiding particular problems. Does Crafty do this however when in analyze mode, >where it is evaluating both sides' play, or is that a symmetric eval? If it's >still asymmetric, how should output be interpreted? No. The asymmetry is turned off in analysis mode so that the score doesn't flip-flop as real moves are made in the game being analyzed. I use this mode on ICC to provide real-time commentary on games being played, and I added the ability to disable asymmetry to avoid the questions that came up when a player made a move and the score went from +1 to -1 because of the asymmetry in the code. > >As an example of what I'm getting at is Stephen Ham's opinion that Fritz' >analysis is more objective, whereas Shredder's is optimistic (for example when >Fritz is showing +0.5 Shredder might be showing +0.8). When using Crafty to >analyze with and it's showing say +0.5, can the user assume this to be a true >half pawn, or does asymmetric eval cause the result to be on the high or low >side, or change with side to move rather than stay fairly stable? > >Ralph in analysis mode the evaluation should be pretty stable, regardless of the side to move...
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