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Subject: Re: A Null Move Enhancement?

Author: Bruce Moreland

Date: 23:32:14 02/10/99

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On February 10, 1999 at 21:55:32, Will Singleton wrote:

>On February 10, 1999 at 19:32:18, Bruce Moreland wrote:
>>On February 10, 1999 at 19:00:03, Dann Corbit wrote:
>>>On February 10, 1999 at 17:20:34, Dan Homan wrote:
>>>>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.
>>>What an incredibly creative idea!
>>Not a new idea ;-)
>Implying that you either use something like this or have found it to be not
>worthwhile.  If you use it, what window value do you use, and does it change
>depending on the situation?

I think the idea is a good idea.  I couldn't make it work in mine, meaning that
it didn't make anything go faster.  I know I've tried it.  I don't think I
invented it.

The idea is obviously that if you are obviously hosed based upon some quick
eval, that you probably aren't going to come back with a fail high if you give
the opponent a free move.

Another idea for you guys, which I didn't invent, tried, and don't use, is
widening the null move window in the downward direction in some circumstances.

You not only check for fail high, and cut off if you get it, you check for fail
low.  A fail low indicates that the opponent has a massive threat.  In this case
you can extend.

This idea was mentioned in the original Donninger paper on null-move, ICCAJ,
don't know what issue, but it was between 1990 and 1995.


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