Author: Gerd Isenberg
Date: 13:18:13 07/02/03
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On July 01, 2003 at 18:10:46, Martin Bauer 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? > >No, hope I am right: > >You evaluate in even at inner nodes. If your static evaluation is already better >than beta, you expect a beta cutoff. So you reduce the remaining depth to get >the cutoff. > >May be there are some extra condiotons for the reduction. > >Martin Hi Martin, yes if ( eval - t >= beta and nullwindow ) then d = d - 1; The threat value t is either computed staticly (inside eval, e.g. en prised and hanging pieces, possible forks, pins, king attacks and other "tactical" heuristics) or by nullmove (quiescence) search. Gerd http://www.talkchess.com/forums/1/message.html?304306
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