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Subject: Re: Null move idea

Author: blass uri

Date: 12:05:46 06/04/99

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On June 04, 1999 at 14:22:24, Heiner Marxen wrote:

>While I agree that "null move" is a good thing, there is
>one disadvantage: it is sometimes wrong, especially in
>zugzwang positions.  This *can* be a problem, although rarely.
>
>I wonder whether this disadvantage can be corrected such,
>that the speed advantage is not given up, but at least
>at greater depths the error is detected/corrected.
>
>My idea: when doing a null move search with depth-R does
>produce a beta cutoff, (and depth-R is large enough,)
>verify the result by another search with depth-R-1 (say),
>with null move suppressed at the top of that search.
>The additional search is reduced in depth, again,
>and hence should not cost more than the null move search
>itself.  And to some extent we would now be more sure,
>that there really exists a legal move which is good
>enough.  And with more depth this would become more accurate.
>
>Is this possible?  Or meaningless?

It is possible but I think that if the program is slowed down by a factor of 2
or 1.5 then  the program is going to be weaker in games because zungwangs are
rare.

I think that it is possible to avoid stupid null move mistakes like not seeing
mate in 2 without doing the peogram weaker.

one simple idea is to use the first 1% of your time for comparing between the
evaluation with null move and without null move.

If you find a big difference in the evaluation then do not use null move in the
search and otherwise use null move.

The program is going to be slowed down by less than 1% but it is going to avoid
stupid blunders that make the users angry.

I think that if the time that you use for comparing between evaluation with null
move and evaluation without null move is small enough and the time for all game
is big enough then the program is going to be slightly stronger in games.

Uri



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