Author: Andrew Williams
Date: 00:33:13 07/31/99
Go up one level in this thread
On July 31, 1999 at 00:06:29, Robert Hyatt wrote: >On July 30, 1999 at 19:33:37, Andrew Williams wrote: > >>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 > > >8 pawn (on one side) positions tend to get blocked. trading one early at least >gives an open file (or half-open) file to fight over. I am seriously >considering a 7 pawn penalty as well to try to trade at least two pawns. But >the risk is simplifying into more drawish positions rather than maintaining >tension... > >The main idea is that computers excel at tactics, not closed positional >stuff... Thanks. Mine doesn't excel at either, so I'll not bother for the time being! Andrew
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