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Subject: Re: null move question(Fruit)

Author: Fabien Letouzey

Date: 04:09:51 07/23/04

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On July 22, 2004 at 20:50:14, Jan K. wrote:

Hi Jan,

>Hi, i have seen in fruit and in other engines too that there is no test if
>(remainingDepth-rFactor-1)>(=)0 before doing null move, only
>remainingDepth>=someConstant, which means making many cutoffs based only on the
>values given by qsearch. That gived a very nice speed up when I tried it, but I
>soon found that my engine makes mistakes in some positions like this one, where
>it shows a draw after <almost every move> <e6e2> <d3c4> <f7g6> <c4d3>, altough
>only <d3c4> doesn't lose(normally seen at depth 5):

About when to try null move, I think "depth >= 2" is the most common.
Most authors haven't had any success with pure null move at depth 1
(static threat detection is possible but is not "null move" IMO).  At
the same time most see benefit in using it at depth 2 and up.

>[D]8/5kpp/4rp2/2p5/PP1p4/3Q2PP/2P2q2/R1B4K w - - 3 30

>it didn't help when I used verification search, checks in qsearch....
>But Fruit doesn't seem to have a problem so do I have a bug or just miss
>something? :))

No hidden trick that I know of.  I tried different combinations of my
null-move parameters and this position was always solved correctly.
All I can say is that when not trying any checks in the qsearch, one
more ply was needed.

I can't reproduce your problem with my engine (with any settings) and
I haven't studied this position.

In general I get the impression that Fruit is relatively quick at
obtaining a draw score, not necessarily correctly.

Don't forget that draw scores are evaluation-dependent.  Draw trees
usually contain side lines with negative evaluation.  The score of one
of these nodes can become positive at larger depth.  Draws are tricky.

Sorry I can't help you more.  Feel free to ask specific questions though.

Fabien.




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