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Subject: Re: Fail high reductions

Author: Ralph Stoesser

Date: 15:19:44 07/01/03

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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.
>
>Uri

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
subtree.

Ralph



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