Author: Tony Werten
Date: 08:02:21 08/12/04
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On August 12, 2004 at 10:52:36, martin fierz wrote: >On August 12, 2004 at 09:28:24, Tord Romstad wrote: > >hi tord, > >thanks for the clarification! so you really RETURN when your >almost_certainly_fail_high function returns true? isn't this a bit dangerous? i >mean, probably it helps, but i can imagine that there are positions where >gothmog will never find the right move because your almost_certainly_fail_high >function returns 1 in a position where it shouldn't. > >my philosophy (in my checkers program, my chess program is not in a stage of >having a philosophy yet...) was always to make big reductions in depth possible, >but never to allow a complete return - because then you can have such effects >that you can never solve a position. Not if almost_certainly_fail_high factors in the remaining searchdepth. ie multiply the margin with the remaining ply left or something. I don't use it myself but I can understand something like that can work. Tony > > >>That recursive null move pruning is not the only kind of pruning I do. >>At fail low nodes, most of the moves are not searched with full depth. >>When the first 3 moves have failed low, I search all remaining moves with >>reduced depth except when they look especially interesting or forcing. >>If a move searched with reduced depth surprisingly turns out to fail high, >>it is re-searched with full depth. >> >>For some reason, most of the published research on selective search >>mechanisms has concentrated on ways to reduce the work at fail-high >>nodes. Nullmove pruning, Multicut pruning and ProbCut are a few examples. >>Pruning techniques for fail-low nodes are much less commonly seen. The only >>ones I can think of is futility pruning and razoring, but these are too >>dangerous to use except when the remaining depth is very small. >> >>Reducing the search depth towards the end of the move list is my own >>attempt to do selective search at expected fail-low nodes. It is >>probably possible to invent better techniques (and it wouldn't surprise >>me if it has already been done in some of the professional engines), but >>at least in my engine, what I do works far better than nothing. > >and thanks for sharing this - another interesting idea of yours :-) > >cheers > martin
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