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Subject: Re: Fail high reductions

Author: martin fierz

Date: 02:47:27 07/02/03

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On July 01, 2003 at 18:24:43, Omid David Tabibi wrote:

>On July 01, 2003 at 18:19:44, Ralph Stoesser wrote:
>>On July 01, 2003 at 18:10:04, Uri Blass wrote:
>>>On July 01, 2003 at 17:34:47, Russell Reagan wrote:
>>>>From "Fail High Reductions by Rainer Feldmann"
>>>>"...a fail high node is a node 'v' with a search window of [alpha,beta] at which
>>>>a static evaluation function 'c' produces a cutoff. The FHR-algorithm reduces
>>>>the search depths at these fail high nodes thus searching their subtrees with
>>>>less effort."
>>>>Their subtrees? I thought fail high nodes didn't have subtrees, and that you
>>>>return beta at a fail high node. I must be misunderstanding something. Could
>>>>someone give a simple explaination of how fail high reductions work?
>>>If I understand correctly the idea is that you evaluate a position that is not a
>>>leaf and the static evaluation is not in the window of [alpha,beta] so you
>>>reduce the depth.
>>>Example:when you analyze e4 Nf6 Qh5 Nxh5 your evaluation is a queen advantage
>>>for black and you can be almost sure of fail high so instead of searching to
>>>remaining depth of 7 you may decide to search to a smaller depth.
>>I think that's right. This is similar to the Nullmove technique, but not that
>>radical, because you only reduce the search depth instead of cutoff the whole
>... which is called verified null-mvoe pruning :)

to me FHR sounds very similar to ProbCut / MultiProbCut, except that it uses the
static eval at a node instead of a shallow search.


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