Author: Albert Silver
Date: 07:46:28 07/30/99
Go up one level in this thread
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
As for myself, I have problems with the comparison of statistics (winning or
losing percentages) with the eval. In the opening, you are judging it from the
results of games (where else can one dig up this 54% ?) which may have little to
do with the objective winning chances of the position. On the other hand, if you
get to an endgame with a slight edge, how do you calculate statistics on it?
Calculate every possible move and then balance out the number of winning moves
to the number of losing moves? Short of hitting the tablebases, I don't see how
this could be done, but since this CAN'T be done in a practical manner, thinking
along these lines is pointless. In the end, you may hit upon a point where the
best move objectively isn't necessarily the move that offers the opponent the
most chances to slip up. Imagine I have a position in which I have a slight
edge. Objectively, I have a move that should keep my edge though not necessarily
increase it, yet I have a complicated trap which renders all legal moves except
one losing. Statistically, this last option gives me the most winning chances,
yet it is hardly the best move, as if my opponent plays that one legal move,
I'll have lost my edge. Of course, if I have two options of equal value and one
of them places a trap, I should go for the trap, but what about when there is a
difference however small? When should you gamble?
Albert Silver
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