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Subject: Re: Verified Null-Move Pruning, ICGA 25(3)

Author: Andreas Herrmann

Date: 12:34:44 11/20/02

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On November 20, 2002 at 15:04:13, Omid David Tabibi wrote:

>On November 20, 2002 at 14:59:10, Andreas Herrmann wrote:
>>On November 20, 2002 at 11:43:10, Omid David Tabibi wrote:
>>>            ICGA Journal, Vol. 25, No. 3, pp. 153-161, September 2003
>>>                          Verified Null-Move Pruning
>>>                    Omid David Tabibi and Nathan S. Netanyahu
>>>                                   Abstract
>>>In this article we review standard null-move pruning and introduce our extended
>>>version of it, which we call verified null-move pruning. In verified null-move
>>>pruning, whenever the shallow null-move search indicates a fail-high, instead of
>>>cutting off the search from the current node, the search is continued with
>>>reduced depth.
>>>Our experiments with verified null-move pruning show that on average, it
>>>constructs a smaller search tree with greater tactical strength in comparison to
>>>standard null-move pruning. Moreover, unlike standard null-move pruning, which
>>>fails badly in zugzwang positions, verified null-move pruning manages to detect
>>>most zugzwangs and in such cases conducts a re-search to obtain the correct
>>>result. In addition, verified null-move pruning is very easy to implement, and
>>>any standard null-move pruning program can use verified null-move pruning by
>>>modifying only a few lines of code.
>>>zipped pdf:
>>>gzipped postscript:
>>Hi Omid,
>>hmm seems interresting. Thanks for the paper. I will try it out in the next
>>days. Did you tryd your null move extension also in pawn endgame positions where
>>the most moves in the search tree are zugzwang?
>No I didn't conduct much experiments on various zugzwang positions. The main
>benefit of verified null-move pruning is in the middle game, since it will
>construct a smaller search tree with more accurate results.
>I believe that in endgames with extreme cases of zugzwang, it might be better to
>turn off null-move altogether; since while verified null-move will guarantee an
>accurate result, the cost of the re-searches might be too much.

i have ask you this because, before about a year i have made several trys to
extend the nullmove with similar extensions like you. But i have mainly searched
a way for using nullmove in pawn endgames while detecting most zugzwangs. I
thought there must be a way to find the right moves if i come deep enough and
without too much code in the eval.

After a lot bad results i'm using again a similar R2/3 nullmove like E.Heinz
with small differences. But i'm using no nullmove in pure pawn endgames. It's
much to risky.

In some days my other computer has time :) (after finishing the current tests)
and i can make some tests with your null move extension.


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