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Subject: null move search reduction factor

Author: Stuart Cracraft

Date: 13:15:44 06/25/04


So, normally in the literature I've read
(and code I've implemented, it's been to
do a null move search with R set to 2,
so search(...depth-1-R).

But in large searches of 8, 9, 10, 11 and
beyond in full width searches, the reduction
of 2 does not seem to help as much as
larger reductions due to the much smaller
subtrees that the null move searches has
to search with an R of 2.

My question is: what have people done
to experiment with larger figures of R and
verify the return value is effective
and horrid moves aren't produced?

I've used R set to ply/2 and ply-2
where ply is the original target depth
of the overall iteration. The savings
in time is substantial and the moves
look the same or as good, the tree searched is
drastically smaller of course, but
I am worried about quality.

Is R of 2 or 3 a holdover from the slow
computing days in the literature and nowadays
you are using higher settings?

Assume everything else about the null move
search is held the same (not done in endgames,
not done in the original position, no more
than 1 null move in a row during the search
without an intervening normal move, etc.)

Thanks ahead,

Stuart



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