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Subject: Re: Null move reductions

Author: Roberto Waldteufel

Date: 18:26:36 10/04/98

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On October 04, 1998 at 19:31:04, Ernst A. Heinz wrote:

>On October 04, 1998 at 19:06:15, Roberto Waldteufel wrote:
>>Hi all,
>>I wonder what reductions various programs use for the null move. I reduce by 2
>>plies, but I believe a one-ply reduction may be more usual. However, I have
>>found R=2 produces quite good results in my program. I would like to hear of
>>others' experiences.
>Below I quote again from my article about "How DarkThought Plays Chess" as
>published in the ICCA Journal 20(3) and electronically available from the WWW
>page of "DarkThought" at URL .
>Search Parameterization
>Null-Move Search.
>      Generally regarded as both a curse and a blessing of
>      microcomputer-based chess programs, the realm of null-move
>      pruning provides ample opportunities for many improvements (e.g. by
>      parameter fine-tuning). In DARKTHOUGHT, null moves may be
>      layered (i.e. disabled in either the upper or lower parts of the search
>      tree up to a predefined depth threshold), made non-recursive or even
>      switched off completely. The first DARKTHOUGHT delayed null moves
>      until depths  <= 5 after Don Dailey (of SOCRATES and STARSOCRATES
>      fame) enthused about this scheme during the 8th WCCC in Hong
>      Kong, 1995.
>      Like many other chess programs, DARKTHOUGHT currently uses a
>      depth-reduction factor of 2 for null-move searches. But other values,
>      especially depth-adaptive ones in combination with various material
>      thresholds for disabling the null move in endgames, are constantly
>      experimented with. The same holds for depth and score margin of the
>      deep-search extension which default to 2 and the value of 3 Pawns
>      respectively.

Thanks for the reply and the extract from your paper. I have read your paper on
extended futility pruning and limited razoring at your web sit today - very
interesting stuff. I currantly do normal futility pruning, but I have not tried
any sort of pruning at depths of 2 or 3. You have given me some good ideas to
try out :-)

Best wishes,

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