Computer Chess Club Archives




Subject: Secrets of Rybka and Fruit from my point of view

Author: Sergei S. Markoff

Date: 14:05:00 12/15/05

1) Fruit.

Fruit search seems to be primitive. "History pruning" is a variation of
well-known idea. After implementing such method in SmarThink some years ago I
named it "history-based pruning" and then changed to "ordering-based pruning".
The outcome of such methods very depends of whole search model, but anyway
history pruning is not the key to Fruit strength.

To my mind, the key of Fruit strength is that the "Chess is the art of
exchange". So, Fabien's idea about flexible game stages looks to be a beautiful
way to improve positional play. Fruit can effectively consolidate the position.
It simply knows when to excange to improve position. I think that it's the main
key (cumulative with very good tuning of evaluation function). I think Fruit is
very perspective. The main line of progress for this project, to my mind, is to
add more complicated knowledge and intellectualize a search.

2) Rybka

Some time ago we discussed with Gian-Carlo Pascutto an idea of create special
"SET-tables" with sets of piece-square values indexed by 1) material on the
board; 2) king position; 3) pawn structure. Such tables can be calculated by
analyzing a lot of games. That time I delayed my work in this area because I
found other perspective things.
You can see that Rybka executable contains a lot of precalculated tables. And
also we all know that Rybka plays positional style. My version is that Rybka
uses some variation of SET-approach. At all cases it uses some precalculated
positional knowledge, but what sort of it? ;)

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