Author: Ricardo Gibert
Date: 10:13:17 01/16/02
Go up one level in this thread
On January 16, 2002 at 12:56:06, James Swafford wrote: >On January 16, 2002 at 07:41:28, Graham Laight wrote: > >I don't have time right now to read all the previous posts, but >I'd like to point out something I thought interesting when >playing with TDLeaf... > >Temporal difference algorithms needs exactly what you mention - >a probability (or a certainty factor I guess) of winning, and >it needs to be in the interval -1 .. 1. Of course -1 = loss, >0 = draw, 1 = win. .9 is 'almost certainly a win', etc. > >You can scale the raw scores from your evaluator and plug >that into a hyperbolic tangent function, and the result of that >will be in that closed interval. What I think is so neat about >using a hyerbolic tangent is that it predicts +5 pawns to >be almost as sure to win as +9 pawns or +15 pawns. If I get >a chance later and you're interested I can throw up a little >chart... it's interesting when you think about it. Say a >1 pawn advantage yields a certainty factor of .74 (I'm making that >up). A 2 pawn advantage might yield a cf of .89, then 3 .95, etc. >The 'obviousness' starts to set it. > >Ok, enough rambling... I've got to get going. What you propose is a tranformation that will not cause an engine to select a different move that it would have without the tranformation being applied. It burns up cpu time with no benefit. Fine for TD, but no help in a regular program. > >-- >James > > >>It has occurred to me that it is wrong to evaluate a position in terms of >>relative pawns (the "de facto" standard - whereby an evaluation of 2 means that >>you're approximately the equivalent of 2 pawns ahead). >> >>This means that many aspects of evaluation have to be squeezed into a dimension >>which is not appropriate at all. >> >>A better way would be to evaluate "winning probability". If a position was a >>draw, the value would be 0.50 (or 50%). If the player should win 3 out of 4 >>times, the eval should be 75%. If the player must win from here, then the >>evaluation should be 100%. >> >>It seems strange when you think about it that all programmers have chosen to >>adopt the traditional "pawn equivalence" standard. >> >>-g
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