Author: Ernst A. Heinz
Date: 11:14:36 07/05/98
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On July 05, 1998 at 03:18:22, David Eppstein wrote: >I found a new idea to add to my program yesterday...one of those >shouldn't-ever-hurt, could make a minor improvement ones. Maybe it's only new >to me, but I didn't see it in a quick look thru the Crafty sources. If it helps >at all, it would only be in tactical positions where a lot of large subtrees >have mate scores. > >My eval has the property that it doesn't ever return a mate score unless it's >really mate (doesn't everyone's? actually it plays a different game than chess >and winning isn't called "mate" but who cares.) So mate scores are special, >they might not be exact due to search extensions but they're always lower bounds >on the true score. > >The new idea is, when I find a mate, save the position in the hash table, and >look it up again later (say in the next round of iterated deepening), if the >hashed mate score is greater than beta, I use it even when the hashed draft is >less than the depth I'm currently searching. The new deeper search would have >found at least as good a score anyway, so you can just cut it off earlier and >save time. Same when eval is negative mate and is less than alpha. > >Stupid huh? No, not stupid at all -- just obvious and straightforward. I have used it with good success in "DarkThought" for a long time. :-) Moreover, I increase the draft of *exact* mate scores by 1 ply which definitely saves some nodes in many positions. =Ernst=
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