Author: Ernst A. Heinz
Date: 17:32:19 01/01/00
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Hi Gian-Carlo, >>Please also note that normal futility pruning at frontier nodes with >>a remaining depth = 1 and extended futility pruning at pre-frontier >>nodes with a remaining depth = 2 are two different flavours of futility >>pruning in the main search. > >The most important difference being that one is sound and the other isn't, >right ? Yes -- the following little table summarizes the according properties. ------------------+-------------------+------------------------------ Futility Pruning | Remaining Depth | Theoretically Sound? ------------------+-------------------+------------------------------ quiescence | -/- | iff margin >= max_posn_score ------------------+-------------------+------------------------------ normal | 1 | iff margin >= max_posn_score ------------------+-------------------+------------------------------ extended | 2 | no ------------------+-------------------+------------------------------ Of course, the soundness properties only hold for the cases of main searches being backed by a quiescence searches with stand-pat cutoffs (which chess programs generally adhere to). >[...] >>Just treat the selective score as a lower bound. Because you did not >>search some moves at all, the real score might actually be better. > >Thanks for the help. I've added the whole bunch to Sjeng and it seems >to give *big* gains with no noticable loss of tactical strength. Fine, independent confirmation is always nice to receive! =Ernst= P.S. "Scalable Search in Computer Chess" now available at MKP online http://www.mkp.com/books_catalog/3-52805-732-7.asp :-) Visit http://supertech.lcs.mit.edu/~heinz/node1.html for more information about the book.
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