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

Author: Omid David Tabibi

Date: 14:45:02 11/20/02

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On November 20, 2002 at 17:39:26, Martin Giepmans wrote:

>On November 20, 2002 at 16:19:29, Omid David Tabibi wrote:
>
>>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.
>>>>
>>>>
>>>>pdf:  http://www.cs.biu.ac.il/~davoudo/pubs/vrfd_null.pdf
>>>>zipped pdf:  http://www.cs.biu.ac.il/~davoudo/pubs/vrfd_null.pdf.zip
>>>>gzipped postscript:  http://www.cs.biu.ac.il/~davoudo/pubs/vrfd_null.ps.gz
>>>
>>>
>>>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
>>plies).
>>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.
>>
>>
>>>Martin
>
>I see that I reduced the numbers of the tables (R=1 ;))
>What I wanted to write is that table 6 is convincing while table 5 is IMO not.
>
>Combining table 4 and 5 my impression is that - from a time perspective -
>R=3 might be better than verified R=2.

(you mean verified R = 3, don't you?!)

Even though standard R = 3 constructs a smaller search tree, the problem with
it, is that it is too risky. Except DIEP which uses a fixed R = 3, I don't know
of any program that uses that value due to its high risk.


>Compared to R=3 verified R=2 solves about 3% more positions but is about 40%
>slower!
>
>Martin



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