Author: Ernst A. Heinz
Date: 11:12:01 08/23/00
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Hi Christophe, >>The "trick" has nothing to do with quiescence search which actually >>is an expensive (non-static) evaluation function. > >Yes it does, Ernst. You cannot consider the QSearch to be a "black box" in this >case, because the tree searched by the QSearch, and the result it yields, >actually depends on the value of alpha and beta. > >So QSearching with a full window will in some cases give a different result >than QSearching with the null window. But this inaccuracy of the quiescence search permeates all the scores produced by a chess program because the quiescence score will also differ for full windows of different widths. Nonetheless, we accept past quiescence scores as correct later on. >> That is why I use >>the general abstraction "horizon_score" for it in my book. > >I agree that this abstraction can be useful sometimes, but in this case I think >you cannot use it. If you are picky and want to stay theoretically sound regarding the scores produced by the quiescence search, you are right. In practice, however, chess programs are not theoretically sound in this respect anyway (see above). Hence, my flow of argumentation about "variable-depth search" being the main reason still stands, at least IMO. >>The negascout "trick" only works for _real_ fixed-depth searches >>_without_ any depth extensions and reductions. As soon as you do >>varibale-depth searches with only nominally fixed depths, the >>research is always compulsory and the negascout "trick" does not >>work because the path lengths below the node in question may be >>much longer than 3 plies until they finally reach the horizon. > >And you can consider the QSearch to be a variable depth search... Right, but above I refer only to the variable-depth nature of the nominal full-width search which is still the main reason for the the negascout trick being not applicable here IMO. I am convinced that a pure non-variable depth brute-force searcher with a standard quiescence search _could_ employ the negascout "trick" without introducing _notably_ more inconsistencies than already caused by the standard usage of quiescence search. Of course, I may be totally wrong here ... =Ernst=
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