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Subject: Re: The superior Rybka chess knowledge

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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