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Subject: Re: When to do a null move search - an experiment

Author: Sune Fischer

Date: 11:25:01 04/26/04

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>(1) you are in some sort of zugzwang position where a null-move will fail high
>for the wrong reason and wreck the search.  Classic examples here are positions
>with very few pieces.  IE pawns vs a knight where the knight can be zugged.
>Most require some minimal amount of material on the board to avoid this problem.
>
>(2) there is a tactical issue that is hidden with the R reduction.  IE the
>classic position with white pawns at f2, g3 and h2, black queen at h3 and black
>pawn or bishop at f3, threatening mate on the move.  If the R reduction prevents
>you from seeing the mate, you can have problems.
>
>(3) The hash table proves that the null-move search will not fail high, meaning
>that the search will be wasted effort.
>
>(4) Obvious positions such as when the side on move is in check.  Not moving
>can't fail high here as the king is lost.
>
>(5) I don't allow two consecutive nulls.  It is a potentially cute way of
>eliminating zugzwang problems, but it is only good for that, and it is not free
>in positions where no zugzwang is possible.  I choose to not deal with it
>although I have this on my "to do" list to test with (say) pawn-only endings.

The first 4 I agree with, unfortunately 1 and 2 are not so easy to detect. :)

I don't get the point of (5) though, how does it avoid zugzwangs?

I don't see any logical reason to do (5), because after you have nullmoved you
want to see if the other side can FH so we may FL on the nullmove. The fastest
way to do that is to do another nullmove.

So I get the same results as Tord here, it's weaker (slightly, but measurably)
with this restriction on.

-S.



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