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Don Dailey

Joined: 29 Apr 2008
Posts: 4323

Post subject: Re: Comparative nodes per second    Posted: Fri Apr 20, 2012 10:57 am

mcostalba wrote:
 bob wrote: Someone has previously suggested, although I have not given it much thought, that I could produce a pretty good eval -> winning percentage formula on my cluster stuff.

This eval <-> winning percentage stuff is really misleading. I don't know from where it came out but a lot of people (normally chess players more then programmers) blindly believes in this fetish. Eval score has no meaning taken as an absolute single number. It has a sense only considered relative to another eval score from another position. So it is just a part of a pair use to compare positions but what counts for the engine search is the pair.

Converting to a win probability is an ill defined concept because win probability is all about your opponent and how he plays and how you play etc... In fact the same position where one side has an advantage has different win probabilities for a pair of strong players vs a pair of weak players in many cases because the advantage may exist only if you have the skill to exploit it.

But it's no worse a concept than eval score and it does attempt to attach a reasonable meaning to it, after all everyone know that the bigger your advantage the better wining chances you have, all other things being equal.

I think you could even improve your chess program by considering this a win probability instead of a score - or at least thinking about it that way. You could take thousands or even millions of positions and index them by type (perhaps by material signature) and track the actual win percentage and you may be able to prove that your program has problems when the actual win percentage does not match the evaluation function converted to win percentage. For a silly example, imagine that your program has the sign wrong for the bishop pair bonus, a serious mis-evaluation issue. If you were to plot on a graph all the positions where one side had a bishop pair advantage, you might find that the win percentage predicted is much lower than the win percentage actually achieved, but only in these positions! That would be a clear sign there was an evaluation problem I would think.

I think it might require a lot of games in order to deal with a lot of noise that would surely come from positional features that did not appear that often but it might be a way to tune a chess program evaluation function.

 Quote: Don said instead an interesting thing, that the same eval is not the same if returned upon searching the leafs or high in the tree.

But as I said, I don't know what to do about that! If you modify the score to account for that you in a feedback loop, you would change the root score. If a system could be worked out I believe there would be many opportunities based on things going on in the tree.
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Larry Kaufman Tue Apr 10, 2012 7:49 pm
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Marco Costalba Fri Apr 20, 2012 5:18 am
Michel Van den Bergh Fri Apr 20, 2012 6:10 am
Miguel A. Ballicora Fri Apr 20, 2012 11:35 am
Re: Comparative nodes per second Don Dailey Fri Apr 20, 2012 10:57 am
Marco Costalba Fri Apr 20, 2012 1:58 pm
Sam Hamilton Fri Apr 20, 2012 2:19 pm
Miguel A. Ballicora Fri Apr 20, 2012 2:29 pm
Don Dailey Fri Apr 20, 2012 3:13 pm
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