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Subject: Re: Null move idea

Author: Dann Corbit

Date: 11:45:22 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 seems it should be useful to at least test it.  I think it should be tested
in two possible scenarios:
0.  Random positions from real games in the beginning, middle, and endgame
1.  Tough problems that have never been solved by chess programs.

From this we might learn that there are places where it can be selectively used,
perhaps.  Or we may be trying to solve problems that are difficult (e.g. we
might make a test suite solver that does one retry with modification of
null-move if the standard search fails).

It might be useful for a "panic mode" in a program that sees it is in trouble.
Perhaps a search that does not throw out null move possibilites will be able to
save the day.

Definitely worth looking into, I think.

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