Author: Gerd Isenberg
Date: 11:28:27 07/02/03
Go up one level in this thread
On July 02, 2003 at 11:09:21, Omid David Tabibi wrote: >On July 02, 2003 at 10:49:41, Gerd Isenberg wrote: > >>On July 02, 2003 at 07:22:00, Georg v. Zimmermann 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? >>> >>>IMHO Rainer Feldmann uses bad terminology. A fail high node is - at least by my >>>definition - indeed a node where one subtree returns a value above beta, you >>>therefor "fail high" and return (value or beta, depending on if you use fail >>>soft). >>>What he intends to say is probably : " a fail high REDUCTION node is a node 'v' >>>with a search window of [alpha,beta] at which >>>>a static evaluation function 'c' produces a cutoff. " >>> >>>The technic he describes sounds a lot more error prone than null move to me, at >>>least in tactical situations. >>> >>>Georg >> >>Hi George, >> >>If i remember well, Rainer Feldmann's FHR is based on the NullMove observation. >>Instead of foreward pruning, FHR reduce depth if a NullMove fail high occurs. > >FHR reduces the depth if static eval >= beta. I think you are confusing FHR with >verified null-move pruning; the latter reduces the depth when null_move_score >= >beta (and cuts off immediately if null_move_score >= beta in the subtree of a >fail-high reported node). > > Hi Omid, I had no access before to "Advances In Computer Chess 8" (1997) page 111-127: Fail-High Reductions R.Feldmann on Page 118: ______________________________________________________________________________ 2. The FHR is based on the NMO. Therefore one could argue that special attention should be given to nodes where the reduced search fails to compute a cut-off. We tested a version of the FHR that re-searched such nodes without depth reduction. This version turned out to be inferior to the original FHR version." 3. The question, whether a better approximation for threats should be used than the static function t, e.g., by doing a null-move quiescence search, is addressed. It turned out that the overhead for the extra searches does not pay off, even if these extra searches are restricted to nodes at leat 3 ply from the leaves. ______________________________________________________________________________ So the point in question seems NMO, whether one use a sophisticated static eval with some threat detections against the side to move or a reduced nullmove search (OK, Rainer wrote null-move quiescence search). Regards, Gerd
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