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Subject: Re: When to do a null move search - an experiment

Author: Vincent Diepeveen

Date: 18:00:22 04/27/04

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On April 27, 2004 at 11:43:36, JosÚ Carlos wrote:

>On April 27, 2004 at 08:37:34, Tony Werten wrote:
>
>>On April 27, 2004 at 03:33:26, Bas Hamstra wrote:
>>
>>>About double nullmove: I tested this in some pawnendgames to see if it could
>>>handle zuzwang problems, but I don't see it perform any better than normal
>>>nullmove. Can Vincent or you post a position where double null outperforms
>>>normal null? I agree the idea is elegant, but I just don't see it work.
>>
>>I switch it off in pawns only endgames. Couldn't figure out why it wasn't doing
>>as well as it sounded.
>
>  I can't think about it now, but I recall this thread where an interesting
>discussion about double null move came up:
>
>http://chessprogramming.org/cccsearch/ccc.php?art_id=241476
>
>  JosÚ C.

Christophe wrote that down just to let you guys believe you should search
fullwidth.

Practical chances of it happening is small, not zero but very close to it.
Additionally you can add a single 'if then else' condition in transposition
table cutoff to avoid the theoretical scenario that christophe describes.

Look the alternative to double nullmove is doing something dead slow like what
Gerd is doing, or what i used to do in my draughtsprogram; a verification
search, which is just a fullwidth search of n-R ply. So not the later posted in
ICGA verification search. Verification search already was excisting in other
publications than in the ICGA. So Omid just stole the name kind of for something
working crappy :)

Basically all those approaches eat shitload of nodes to say it *very* polite.

Also expensive is just turning off nullmove with little material left.

Way easier is Double nullmove. Note that a few years ago (1997 or so) i used
different Reduction factors. First one was 3, second one 2 and third one 1 near
the leafs to not go into qsearch too soon. A similar variation was later called
by Ernst adaptive nullmove.

Nowadays i use simply R=3 for nullmove everywhere, also when done after each
other.






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