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Subject: Re: Recursive Null-Move Pruning

Author: Robert Hyatt

Date: 10:22:31 07/08/02

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On July 08, 2002 at 13:07:06, Omid David wrote:

>Although the risks of using null-move pruning in the recursive way (several
>times along a variation), are not so high, I didn't get great savings (reduced
>search effort) from it. To the best of my knowledge in the eraly 1990s no
>program used recursive null-move search. What's the standing now?


The problem in the late 80's was "depth".  IE Cray Blitz could search about
9 plies deep at that point, maybe 10 max.  allowing multiple null-moves in
a single path could hide important tactics and cause errors.  R=2 had the
same effect.  Since nobody (except for the "monster machines" like Cray
Blitz, Hitech and deep thought) could search to 9-10 plies, the rest were
even more likely to experience problems.

Today, null-move users are in two camps:

1.  R=2, recursively applied.

2.  R=2~3 (dynamically adjusted) recursively applied.  I don't know of anybody
today that is only allowing exactly one null-move in any distinct path, as was
done in the late 80's and early 90's.



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