Author: Dave Gomboc
Date: 09:46:17 08/13/99
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On August 13, 1999 at 10:22:59, Ulrich Tuerke wrote: >On August 13, 1999 at 02:19:30, Scott Gasch wrote: > >>Hey, >> >>I have a (stupid?) question about aspiration search. I understand the concept >>is to atrificially limit the search window in an effort to prune faster. >>However, a value returned from Search(pos, a, b) will always be within the a-b >>window. I.e. a <= value <= b. How, then, does one tell if the value returned >>is bogus and needs to be re-Searched or whether it is good? Which does a value >>== a or value == b mean? >> >>Thanks, >>Scott > >Usually, the search window is defined without the boundary, i.e. >a < value < b is an exact score; a = value or b = value means that you have >to proceed a verification search. > >BTW, the alpha beta search of my program returns also values far outside the >alpha-beta region; these can be taken as bounds for the verification search. >I think that I remember vaguely that there are 2 kinds of alpha-beta >implementations: "fail soft" and "fail hard". I think that "fail soft" always >returns a value a <= value <= b ? >It seems that you are using "fail soft" whereas I use "fail hard". > >I am sure that Bob Hyatt can help. > >Regards, Uli It's the other way: "fail hard" means that the score will be held within the range [a,b], but and "fail soft" will return a score outside the range [a,b] on occasion. Dave
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