Author: Robert Hyatt
Date: 15:54:18 03/16/03
Go up one level in this thread
On March 16, 2003 at 18:32:01, Ralph Patriquin wrote: >On March 15, 2003 at 23:06:00, Robert Hyatt wrote: > >>>>On March 14, 2003 at 16:58:15, Uri Blass wrote: >>>> >>>>>No >>>>> >>>>>I know that Crafty has anti symmetric evaluation and it means that it is >>>>>relatively bad in these positions because it may try to open the position also >>>>>when it is wrong. >>>>> >>>>>I prefer to use an objective program to analyze games and not a program that >>>>>tries to avoid closed positions. >>>>> >>>>>Uri >>>> >>>>Fine. Which program gives the right answer in such positions then? None I >>>>know of. >>> >>> >>>Which human gives the right answer in such positions? Nobody's perfect. >> >>The point was, however, that if asymmetry for such problems is _bad_ then >>which program without asymmetry does it well? I'm not aware of any that >>don't have problems with blocked positions. It's the way the "draw masters" >>do their evil on ICC. :) >> >> >> >>> >>>As an aside, it is worth pointing out that DB2 did not do too badly in that >>>closed Ruy game against Kasparov, where Kaspy resigned in a drawn position. >> >>Correct, but who knows how they did it? The idea for "asymmetry" is well- >>known. >> > >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...
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