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

Author: Omid David Tabibi

Date: 13:19:29 11/20/02

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On November 20, 2002 at 16:04:50, Martin Giepmans 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:
>If I'm not mistaken this is the well known "verification search" with
>one modification: no verification in the verification search.
>Am I right?

The classical verification search as introduced by Plenkner comes to detect
zugzwangs. Verifeid null-move pruning as presented in the paper, constructs a
smaller search tree with greater tactical strength in middle games (in addition
to detecting zugzwangs).

>Another question:
>your results in table 5 seem convincing, but what about table 4?
>Are these results statistically significant? (my guess is no ..)

For a good estimate of the growth of the search tree as we go deeper, see Table
3 and Figure 4 (which present ECM test positions searched to a depth of 11
The WCS test positions were mainly used for testing the tactical strength
(results in Table 5). Table 4 was provided just for the sake of completeness.


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