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Subject: Re: Verified Null-moving

Author: martin fierz

Date: 07:52:36 08/12/04

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On August 12, 2004 at 09:28:24, Tord Romstad wrote:

hi tord,

thanks for the clarification! so you really RETURN when your
almost_certainly_fail_high function returns true? isn't this a bit dangerous? i
mean, probably it helps, but i can imagine that there are positions where
gothmog will never find the right move because your almost_certainly_fail_high
function returns 1 in a position where it shouldn't.

my philosophy (in my checkers program, my chess program is not in a stage of
having a philosophy yet...) was always to make big reductions in depth possible,
but never to allow a complete return - because then you can have such effects
that you can never solve a position.


>That recursive null move pruning is not the only kind of pruning I do.
>At fail low nodes, most of the moves are not searched with full depth.
>When the first 3 moves have failed low, I search all remaining moves with
>reduced depth except when they look especially interesting or forcing.
>If a move searched with reduced depth surprisingly turns out to fail high,
>it is re-searched with full depth.
>
>For some reason, most of the published research on selective search
>mechanisms has concentrated on ways to reduce the work at fail-high
>nodes.  Nullmove pruning, Multicut pruning and ProbCut are a few examples.
>Pruning techniques for fail-low nodes are much less commonly seen.  The only
>ones I can think of is futility pruning and razoring, but these are too
>dangerous to use except when the remaining depth is very small.
>
>Reducing the search depth towards the end of the move list is my own
>attempt to do selective search at expected fail-low nodes.  It is
>probably possible to invent better techniques (and it wouldn't surprise
>me if it has already been done in some of the professional engines), but
>at least in my engine, what I do works far better than nothing.

and thanks for sharing this - another interesting idea of yours :-)

cheers
  martin



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