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

Author: Omid David Tabibi

Date: 15:49:15 11/20/02

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On November 20, 2002 at 18:39:13, Martin Giepmans wrote:

>On November 20, 2002 at 17:45:02, Omid David Tabibi wrote:
>
>>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
>
>Yes, of course I mean verified R=3 (I did it again ;)).
>
>What about my last remark (the percentages)?
>From a time perspective your results may indicate that vrfd R=3 is actually
>_worse_ than R=3.
>OK, R=3 is risky, but for the prize of an occasional oversight (3%) you get
>a speedup of about 40% (according to your tables).
>The prize for 40% speedup is 1 or 2 extra plies in 3% of the positions ...
>I think if you do the math you will see that that is very cheap.
>
>In a tournament game with clocks R=3 is indeed risky. One oversight is often
>enough to lose a game. The question is how a (less risky) combination of R=2 and
>R=3 compares to your method.
>

By "combination of R=2 and R=3" you mean adaptive null-move pruning, don't you?
Verified version has a greater average tactical strength than standard R=2 (and
thus greater than adaptive R=2~3), and its tree size is smaller using simple
quiescence search.

And don't forget that using verified null-move pruning, you detect the zugzwangs
and end up with the correct result, while in standard version you don't.


>Martin



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