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Subject: Re: Winning Chances vs Material/Positional Evaluation

Author: Andrew Williams

Date: 16:33:37 07/30/99

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On July 29, 1999 at 23:33:08, Robert Hyatt wrote:

>On July 29, 1999 at 19:44:55, Amir Ban wrote:
>
>>On July 29, 1999 at 09:29:32, Robert Hyatt wrote:
>>
>>>On July 29, 1999 at 08:25:58, Chris Carson wrote:
>>>
>>>>On July 29, 1999 at 07:16:32, Amir Ban wrote:
>>>>
>>>>>On July 28, 1999 at 18:16:24, Dann Corbit wrote:
>>>>>
>>>>>>On July 28, 1999 at 17:50:51, Kristo Miettinen wrote:
>>>>>>
>>>>>>>The position is the opening array, all pieces in their initial positions. The
>>>>>>>explanation about the eight pawns makes sense, intending to steer Crafty into
>>>>>>>open waters (on the assumption that the opponent is human?)
>>>>>>>
>>>>>>>I was looking into this on a whim, as I use the advantage of White in the
>>>>>>>opening position as my quantum of positional value (on which scale the value of
>>>>>>>a pawn is 6 quanta for me).
>>>>>>Here is the C.A.P. record for that position.
>>>>>>
>>>>>>rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - acd 15; ce -7; pv e4 e6 Nf3
>>>>>>Bb4 Nc3 Ne7 Bc4 Nbc6 O-O O-O d4 Bxc3 bxc3 Na5 Bb5; pm e4; id "C.A.P. 4028";
>>>>>>
>>>>>>I bet you never knew crafty was French.
>>>>>>
>>>>>>Crafty thinks it is behind by 7 one hundredths of a pawn.  This is obviously
>>>>>>conservative because white has a tempo at least.  But I don't think that it is
>>>>>>grossly inaccurate.
>>>>>
>>>>>A correct evaluation is one that matches the winning percentages of the
>>>>>position. I think white has about 54% in serious play, and if so the evaluation
>>>>>should be about +0.20.
>>>>>
>>>>>Amir
>>>>
>>>>Amir,
>>>>
>>>>Interesting point.  If I read you correctly, the "Evaluation" should match
>>>>the winning changes.  This is not the way most programs "Evaluate" a position.
>>>>Granted that a higher "Eval" by a program should mean a higher "Chance" to
>>>>win, it is normally not a "Percentage" based on results.
>>>>
>>>>I have thought that this might be a better method of "Evaluation", some
>>>>programs do use a "Percentage" (Crafty) for opening book moves, but not
>>>>for middle game or end game positions.
>>>>
>>>>Any thoughts on how to incorporate "Percentage" into the "Evaluate" function
>>>>of a program (knowledge)?  Perhaps a "Percentage" "Evaluation" for positions
>>>>and endgames as a part of the learning (Crafty might be able to do this)
>>>>would be useful.  Any comments?
>>>>
>>>>Best Regards,
>>>>Chris Carson
>>>
>>>
>>>I disagree.  Evaluations are not 'absolute' any more than FIDE Elo ratings are
>>>absolute.  The correct evaluation is the one that lets you _win_ 54% (or better)
>>>of the games from the opening position.  Whether the starting score is +1.00 or
>>>-1.00 is immaterial so long as you choose the best move(s) by using those
>>>scores...
>>
>>This is to answer several posts in reply to my original comment:
>>
>>Evaluations need to represent winning chances in some way, or else there's not
>>much use for them. It's true that the object of all this is to play good moves,
>>but to say that is to beg the question of how to evaluate positions so as to
>>play good moves.
>>
>>There are many ways to do this mapping. Obviously you can multiply the eval by a
>>factor to choose your scale, and you can also add a constant without changing
>>much, but an additive constant is suspect if you define a 0 evaluation to be
>>equivalent to a draw or 50% outcome. As long as your mapping is monotone in
>>winning chances, and your draw score is calibrated correctly, it's good.
>>
>>Practically, almost everyone agrees on scale by calling a pawn advantage about
>>1.00 (on average). Assuming some smooth mapping (there are exponentials that are
>>natural to use), to say that 54% maps to +0.20 is not so arbitrary as some
>>commented, though if someone insists it's +0.15 or +0.30, I won't argue. A minus
>>score, though, obviously doesn't fit because it has the wrong sign.
>>
>>The problem with having incorrect evaluations (not monotonic, or wrong sign) is
>>obvious with some thought: the program may prefer a bad position to a good
>>position (which always involves playing a bad move ...), or may accept a draw
>>when ahead.
>>
>>Our evaluations may be bad regardless, because our knowledge of the game is
>>incomplete, but there's no reason to accept a logical inconsistency in the
>>evaluation.
>>
>>When I talk about winning chances I'm not referring to any specific database
>>information that is available, but about an objective (and usually unknown)
>>outcome of the position.
>>
>>Amir
>
>
>I wouldn't begin to argue... but two points...
>
>(1) a minus score for white's first move can be considered bad...  in that we
>all agree that white has better winning chances than black.  So for those that
>want to take a program's 'evaluation' of a position as gospel, then - is
>confusing at best, and misleading at worst...
>
>(2) a minus score for white's first move can be reasonable, if a program has
>some asymmetry in the eval.  IE I use Belle's idea of '8 pawns is bad' and
>until one is exchanged, crafty gets a small penalty whether it is playing black
>or white.  And if white,  it is possible that it can find a PV where no pawn
>exchange occurs and yet it can't find a developmental/positional advantage to
>offset that 8-pawn penalty.
>

I fear I am being dense here, but what is wrong with having 8 pawns?


>I do, on occasion, look at positional scores and ramp down or ramp up if I
>believe the number is 'out of line'.  But I am more interested in the move the
>eval leads it to play, because that is the critical issue in winning games...
>
>I think most programs are pretty naive positionally, mine included, and often
>see scores that make little sense.  For any program...


Andrew



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