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Subject: Re: Fail high reductions

Author: Ralph Stoesser

Date: 16:34:28 07/01/03

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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.
>>>
>>>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.
>
>... which is called verified null-mvoe pruning :)
>
>>
>>Ralph

Now, after I have read your interesting article about it, I would tend to agree
:)



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