Computer Chess Club Archives




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

Author: J. Wesley Cleveland

Date: 09:40:21 04/27/04

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On April 26, 2004 at 12:14:33, Josť Carlos wrote:

>On April 26, 2004 at 11:57:43, Vincent Diepeveen wrote:
>>In *all* experiments i did with nullmove and a program not using *any* forward
>>pruning other than nullmove, the best thing was to *always* nullmove.
>  Yes, that's what other programmers also said (including me) in the thread we
>had last week. That's pretty intuitive. With not any other forward pruning (or
>very little) but null move, the cost of not trying a null move that would have
>produced a cutoff it terrible compared to the benefit of saving an useless null
>move try. So avoid null move, in this case, must be only in a very few cases
>where you're 99.99% certain you'll fail low... if any.

This seems way too conservative. With R=3 and a branching factor of 4, a null
move should use 1/64 the nodes of a full width search, so if you are 99%
confident you'll fail low, avoid the null move. Fortunately, null move questions
are easy to test. When you would avoid a null move (or skip a full search), set
a flag, make the null move (or full search) anyway, and increment one of two
counters depending on whether the result is the one you expect.

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