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Subject: Re: The superior Rybka chess knowledge

Author: Uri Blass

Date: 11:04:56 01/18/06

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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
>Insofar is the Rybka approach intelligent ignorance.
>P.S.: The omission of Piece-Square-Tables is a feature of Hydra. I do not state,
>that Rybka as skipped this feature too.

I think that most programs are going to be weaker if you remove piece square
tables without doing more changes.

I believe that mobility evaluation is usually done after piece square table and
it is going to be too small if you remove piece square tables without doing more
changes like increasing mobility.

I guess that usually programs evaluate knight at the centre of the board as more
important both because of piece square table and because of mobility.

I guess that in most cases if you remove piece square table then the mobility
evaluation of knight at the centre of the board is not going to be big enough
and the program is going to play weaker.


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