Author: Ernst A. Heinz
Date: 11:38:05 12/07/00
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Hi Bert, >In a previous question about Futility pruning Vincent Diepeveen mentioned: > >>Futility pruning is very dubious. It sure speeds you up, but it's >>dubious and tends to give you slight positional >>differences that make a program play positional >>a lot weaker. > >Can sombody explain me why Futility pruning tends to give slight positional >differences? Vincent's statement is just wrong for futility pruning at frontier nodes which is theoretically sound for suitable "max_posn_score" margins, given that the search allows for "stand-pat" beta cutoffs at horizon nodes (which typical quiescence searches usually do). I have already explained this several times here and in my publications but, unfortunately, Vincent does not seem to understand. For more detailed information, please read my article on extended futility pruning in the ICCA Journal (a preprint thereof is available from my WWW pages at http://supertech.lcs.mit.edu/~heinz/). However, if you use aggressive futility margins, the forward pruning becomes selective and might erroneously cut moves that actually affect the value of the frontier node in question. As Bob already pointed out, selective pruning always tends to lead to differences of *any* kind (i.e., not only positional but also tactical ones). =Ernst=
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