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Subject: A Null Move Enhancement?

Author: Dan Homan

Date: 14:20:34 02/10/99

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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
>>instantly...
>>
>>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
>>easy...
>
>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
>cutoff.

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.)

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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