Computer Chess Club Archives




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

Author: Stuart Cracraft

Date: 14:08:05 12/20/05

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On December 20, 2005 at 00:19:22, Vincent Diepeveen wrote:

>On December 16, 2005 at 03:32:16, Vasik Rajlich wrote:
>>On December 16, 2005 at 00:56:04, Zappa wrote:
>>>On December 15, 2005 at 17:05:00, Sergei S. Markoff wrote:
>>>>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? ;)
>>>My personal opinion:
>>>Fruit wins by 3 things: deep PV checking, mobility, and correctness.  I talked
>>>about this with Fabien at Reykjavik.  When you have mobility, you are very
>>>sensitive to being "driven back".  And when you can check your mainline 18-20
>>>ply and not lose any mobility, its very probably you're playing a good move.
>>>Rybka: I'm starting to think that a lot of Rybka's strength is tactical.  Try
>>>that baby out on a few test positions some time.  For example, the rapid TC CEGT
>>>list has Rybka 55 rating points ahead of Fruit, while the slower BFF list has
>>>Rybka only 15 rating points ahead of Fruit.
>>We need more data. I'll try to put it together when it's all ready.
>>One thing people tell me is that Rybka tends to stick with her moves from lower
>>depths more than other engines. This would also suggest better blitz play.
>In past programs sticking to the same move and showing same mainline was very
>common. We called it back then preprocessors.

This is interesting. So if I toss the preprocessor, put in the same
evaluation in the endpoint evaluation instead, my initial move in each
iteration will more frequently change.

That is interesting.

I hope I did not misunderstand that.

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