Computer Chess Club Archives




Subject: Re: Fail high reductions

Author: Omid David Tabibi

Date: 15:24:43 07/01/03

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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 :)


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