Author: Peter McKenzie
Date: 01:19:45 01/27/99
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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 If you are at depth=2, 2 plies from the leaves, don't you have TWO more ply of full-width search left? >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. This sounds like what I described in an earlier post, which I'm told is called Futility Pruning. Or perhaps I'm missing something here?? > >works pretty well most of the time, and speeds the search by 25-50% generally.
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