Author: martin fierz
Date: 07:52:36 08/12/04
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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. >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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