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

Author: Uri Blass

Date: 12:49:39 12/16/05

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On December 16, 2005 at 15:35:55, Vasik Rajlich wrote:

>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.

I remember that there was some experiment with Fritz6 that showed diminishing
returns and it also logical.

Previous experiments also supported diminishing returns but the results were not

I think that it is obvious that some opening lead to forced draw and it is going
to be draw only if the sides search deep enough so after some time control there
is 0 returns in these openings.

It means that in order not to have diminishing returns you need to have opening
with increasing returns.


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