Author: Ralph Patriquin
Date: 22:14:38 03/16/03
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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? 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
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