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

Author: Robert Hyatt

Date: 11:06:37 01/16/02

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On January 16, 2002 at 12:58:13, James Swafford wrote:

>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


It could be linear.  But perhaps the slope of the straight line is not 45
degrees...



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