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Subject: Re: Evaluation Should Be Winning Probability - Not Pawns

Author: James Swafford

Date: 09:58:13 01/16/02

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On January 16, 2002 at 11:43:59, Robert Hyatt wrote:

>On January 16, 2002 at 07:41:28, Graham Laight wrote:
>
>>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
>
>
>It is harder to do otherwise.  IE KPP vs K is winning, except for some rare
>cases, while KR vs KB is drawn.
>
>It would be very hard to translate some sort of material imbalance into a
>winning percentage.  As a general rule, the more material you are ahead, the
>better your chances, with some exceptions that many engines know about...

Right, but the gains are not linear, and raw scores from an evaluator
typically are.  Winning probability is not a linear function of material
+ positional advantages.

--
James





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