Author: Uri Blass
Date: 22:41:03 01/19/06
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On January 19, 2006 at 18:18:44, enrico carrisco wrote: >On January 18, 2006 at 13:34:17, Chrilly Donninger wrote: > >>After playing several engine matches against Rybka (chess programming is a >>rather boring job) I have come to the conclusion: There are a few special >>evaluation features of Rybka which are really unique. It is interesting that >>some seamingly relative unimportant feature appear regularily on the board. The >>opponent has no idea of this feature and does not prevent it. And the search >>always finds a way to reach the pattern. Rybka has e.g. some special passed pawn >>evaluation terms. I do not want to tell the details, but the game Zappa-Rybka, >>Paderborn 2005 is a prototype game for one of these special features. >>But the main chess-knowledge which sets Rybka appart from other engines is >>ignorance. The omission of features which other engines have incorporated. >>I have written a longer article for the German "Schachkalender 2006". The >>message of this article is: Most of the published chess knowledge is completly >>useless. Give your favorite chess-enemy your chess-books as a present. They will >>do some harm on his play. >>Rybka seems to be to prove of this hypothesis. If a feature is - in a given >>position - correct, it is of course an advantage if a programm has implemented >>it. But if its wrong, the programm hangs on an advantage which does no really >>not exist. Or even worse, it sacrificies another advantage to reach the pattern. >> >>I realized the principle: "It is sometimes more important to remove features >>than to add ones" several times in the Hydra project. E.g. Piece-Square Tables >>are generally considered as a "must have". Strong Chessplayers do not like them. >>It is very unnatural for them to evaluate a piece without considering the >>context of the other pieces. It took some time till GM Lutz convinced me to >>remove them in Hydra. And indead, the programm played considerably stronger with >>Piece-Square. >>Insofar is the Rybka approach intelligent ignorance. > >Hello. > >Let me restate what you have written and add some of my own points (some of >which I have stated here previously, in other Rybka threads...) > > >So you think Rybka is a fast searcher with little knowledge... :) Well, I don't >dispute that (in fact I've claimed it many times in past threads...) >http://jbo.gotdns.com/chess/fast-rybka.jpg I do not agree. Size of evaluation is not important. The evaluation function of rybka is very good. I have objection to describe program as having little knowledge based on size of evaluation. > >However, what it _does_have_ is a very well tuned evaluation which seems to be >correct 99.9% of the time. Why? It concentrates on what is known to be >successful in chess. It speculates in evaluation on a few things: passed pawns >and activity -- and this is obvious by the short (and sometimes long) pause, >often with no search information being updated (position recognition/bit board >access.) Couple this with the fast search and it often makes these count. > >Rybka uses an invisible Genius-like search to protect itself from tactical >mistakes and sooner or later, when you are searching very very fast and deep, >your opponent will go wrong. The extra search (especially when not included in >its definition of a node) makes it appear like it has more knowledge and that is >clearly what sells chess programs (ex: low nps display...) I do not agree about it. People buy rybka because of the fact that it simply beats other programs regardless of nodes per second. > >Clearly you have a point that wrong knowledge is much worse than no knowledge >because it means you trade one possible real advantage for a different but >unreal advantage. No It mean that you trade speed advantage by real disadvantage of worse evaluation. > Also, in computer chess, if you are outsearched it can look >ugly. My impression is that rybka simply has evaluation advantage relative to other top programs. I simply saw positions when rybka was more correct in evaluation relative to other programs that I tried like shredder fruit and fritz. Uri
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