Computer Chess Club Archives




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

Author: Robert Hyatt

Date: 07:59:26 12/16/05

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On December 16, 2005 at 01:47:14, Stuart Cracraft wrote:

>On December 15, 2005 at 21:52:49, Robert Hyatt wrote:
>>On December 15, 2005 at 21:01:00, Brian Richardson wrote:
>>>On December 15, 2005 at 20:03:47, Sergei S. Markoff wrote:
>>>>>Really? Just the line from fruit:eval.c:
>>>>>  eval = ((opening * (256 - phase)) + (endgame * phase)) / 256;
>>>>No. Not just this line, but the concept and well tuning.
>>>>>I find that VERY hard to believe. That concept has been around a
>>>>>very long-time.
>>>>Really? Where it was introduced by the first time?
>>>Don't know about the first time, but GNUChess (v4) uses the same approach,
>>>albeit only for some king eval terms, and many programs scale things by
>>>material, although not necessarily as nicely as Fruit does.
>>Most all programs use something similar.  You can't afford to have
>>discontinuities in the evaluation or when you are in positions that are right
>>around the discontinuity, you will get some really bizarre results as the search
>>will find ways to creatively cross over the discontinuity when it seems
>>favorable, to produce a big score change over nothing.
>Bob - this is a *great* explanation. Good reason to implement it asap.

As I said, it has been known for years.  Berliner was the first to put it in
writing that I know about, but most everyone has stumbled over this at some
point, and it causes great problems...

>>Crafty has lots of terms that "scale" by material.  Kingsafety drops off as
>>material goes away.  Endgame features (pawn majorities, outside passed pawns,
>>etc) scale up as material goes away.  This is not new...  I think Berliner first
>>mentioned this "problem" 25 years ago in some paper or another...

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