Computer Chess Club Archives




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

Author: Vasik Rajlich

Date: 12:35:55 12/16/05

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On December 16, 2005 at 13:34:43, Uri Blass 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.
>I think that it may suggest simply that rybka is better because it needs less
>time to find the correct moves unlike other engines that need big depth to find
>the correct moves.
>I think that the only correct test is test with time handicap.
>I think that it may be interesting to see how much time programs need to get 50%
>against Rybka at 1 minute per game and the same for longer time control.
>I think that there is diminishing returns so if a program score better at blitz
>but wins at all time controls then it is not fair to claim that it is better
>blitz player.
>If you can prove that Rybka score 50% with time handicap of 3:1 at blitz against
>engine X(ponder off) and score less than 50% with the same time handicap at
>longer time control then you have a point.

Another topic we need some data about. Was it ever proven that engine
differences are magnified at shorter time controls? It's not obvious to me.


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