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Subject: Re: A Null Move Enhancement?

Author: Dan Homan

Date: 05:12:05 02/11/99

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On February 10, 1999 at 17:20:34, Dan Homan wrote:

>On February 10, 1999 at 14:54:43, J. Wesley Cleveland wrote:
>>On February 09, 1999 at 22:59:52, Robert Hyatt wrote:
>>>one of the big 'time savers' is what happens _below_ a sacrifice for nothing.
>>>Qxp pxq.  And now no matter what two moves white plays in a row, black's
>>>position is still 'good' and everything below such moves gets trimmed away
>>>IE with a full-width search, there are _many_ captures that are losers.  Null
>>>move reduces the depth below these moves and make dismissing them quick and
>>This makes me wonder whether null move is even worthwhile if there is not a
>>large material difference. I would think that with even material null move would
>>be much less likely to produce a cutoff and much more likely to give a false
>This is a very interesting observation.  Maybe it would be right to
>say that null move might be a "waste" of time if the material score
>is not close to beta?  Taken a step further... some kind of a "windowed"
>null-move might be a good idea.
>I tried this in my program.  I changed my null move code so that
>a null move would only be tried *only* if the material score for the side
>to move was greater than (beta-1.5*pawn_value).  This reduced my
>searched nodes from 5-10% in most of the positions I have tried so
>far.  (I have only tried a handful of WAC positions so far.)

Ok,  I tried the full WAC set.  Overall the improvement is 0% to 5%
depending on the position.  Most positions seem to search a few %
few nodes to reach the same depth.  This is all with the 1.5 pawn
window.  In the end, I went from 277/300 in 5 seconds per problem
to 278/300 in 5 seconds per problem.  This is all on my 400 MHz

 - Dan

>If this pans out, It is a perfectly safe enhancement to
>null-move.  The 1.5 pawn window that I tried was arbitrary;
>another value might do better.
> - Dan

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