Computer Chess Club Archives




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

Author: Robert Hyatt

Date: 19:30:15 04/27/04

Go up one level in this thread

On April 27, 2004 at 12:40:21, J. Wesley Cleveland wrote:

>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.

That math can't be right.  at best it saves 1/16th the nodes, because not
_every_ ply is full-width.

> 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.

This page took 0.01 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.