Author: Robert Hyatt
Date: 06:08:15 01/27/99
Go up one level in this thread
On January 27, 1999 at 04:11:42, Amir Ban wrote: >On January 26, 1999 at 22:08:21, Robert Hyatt wrote: > >>On January 26, 1999 at 15:02:10, Peter Fendrich wrote: >> >>>On January 26, 1999 at 11:56:50, Steve Maughan wrote: >>> >>>>I've heard of this technique but am not sure exactly what it is. Could someone >>>>please explain it? >>>> >>>>Regards >>>> >>>>Steve Maughan >>> >>>Like the term "selective program" I don't think there is only one definition. >>>The first time I heard about razoring in chess programs was in the article: >>>"Tree-Searching and Tree-Pruning Techniques" by John Birmingham and Peter Kent >>>at 1977. It was in "Advances in Computer Chess 1" wich I don't have but I got >>>the article from some other book. >>>They described razoring like this: >>>1) In a node make and search the first n (few) moves. >>>2) The rest of the moves are first evaluated by the static evaluator. If the >>>evaluator didn't reach alpha they just skipped the move instead of of searching >>>it. >>> >>>At that time it probably was a good idea when the programs reached a few plies. >>>This old style of razoring is better done by Null moves today, IMHO... >>> >>>A more modern approach can be found at Dark Thought's site, especially at the >>>page: http://wwwipd.ira.uka.de/Tichy/DarkThought/node29.html >>>They just shortens the depth if the razoring condition is true. >>> >>>//Peter >> >>The only definition of razoring I remember seeing is the one I use in Crafty: >> >>If I am at depth=2 (2 plies from the leaves, IE I have one more ply of >>full-width stuff to look at before I drop into the q-search code) and the >>current move is not 'interesting' (not a check, etc.) then I reduce the depth >>by 1 extra ply which means I drop right into quiesce. I only do this if the >>move is uninteresting, and the static eval (including material) is so far below >>alpha that 'uninteresting' moves have little chance to bring it back up to a >>point where it won't fail low. >> >>works pretty well most of the time, and speeds the search by 25-50% generally. > >But this is just futility pruning, which I guess most everybody does. Razoring >is supposed to be a sort of forward pruning where rather than skipping an entire >subtree, you search it to a reduced depth, typically one less than normal depth. > The advantage is that you get most of the saving but with much lower risk than >pruning entire subtrees. > >Razoring is the only forward pruning technique Junior uses, with a depth >reduction of one (half-ply). > >Seems like Crafty uses the same definition. Grep the source and you'll find this >comment: > >/* > ---------------------------------------------------------- >| | >| now we toss in the "razoring" trick, which simply says | >| if we are doing fairly badly, we can reduce the depth | >| an additional ply, if there was nothing at the current | >| ply that caused an extension. | >| | > ---------------------------------------------------------- >*/ > >Amir I'm confused... is my definition of 'razoring' right or wrong? This idea came from an old JICCA although I don't remember which, as this was written about three years ago I think... But I am definitely not 'pruning' because I don't just toss the move (I have tried that some as well but didn't like the result. I got a lot faster, but I found problems in wild positions, just where I don't need problems.)
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