Author: Ulrich Tuerke
Date: 08:29:35 10/28/99
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On October 28, 1999 at 08:42:50, Rémi Coulom wrote: >On October 28, 1999 at 06:30:37, Ulrich Tuerke wrote: > >>On October 27, 1999 at 15:38:54, Frank Schneider wrote: >> >>>Hi all, >>> >>>this is a question about the searchalgorithms used by other programs. >>>Many programs and also Gromit seem to use PVS or MDT(f) which both use >>>nullwindow-searches. >>>Is there anyone using a search that doesn't do nullwindow searches? >>>Why? Why not? >> >>I am sure that there are some programs not using minmal window searches, also >>among the top programs (Hiarcs ?). >>In principle (AFAIK), the AB standard algorithm works correctly, PROVIDED the >>result of the search does not depend on the choice of alpha and beta. >>However in practice, this condition may be violated in most cases. Think for >>instance of evaluation window techniques, null move cuts, futility cuts, >>extensions, ... . >>The violation of this precondition can make the search instable, e.g. you may >>get a fail-low in a fail-high verification search, because alpha & beta have >>changed when doing the re-search and the conditions for your tactical extensions >>will not be reproduced in some cases. >> >>When it now comes to a minimum window search, you have generally many more >>verification searches with shifted aspiration window. Thus, the above described >>instabilities may become far more dramatic. Of course, this happens not only on >>the root of the search, where it becomes obvious but also internally (in PVS) >>all the time. In my prog, I observed that I do not get stable evaluations at all >>when using PVS, though it fastened up the search a little bit. I think that this >>was a consequence of the very strong alpha-beta dependencies in my prog. >>Therefore, i decided not to use PVS. >> >>Uli >>> >>> >>>Frank > >I have the same problem in The Crazy Bishop. One idea that might be worth trying >would consist in using two windows in a search : the real alpha-beta window and >the aspiration window. Beta cutoffs on the aspiration window would be allowed >only in case there is a real move >= AspirationBeta, I am afraid that this would kill the performance of your prog, because you skip lots of cuts ! Uli >the null move being tested >against RealBeta only. This is on my list of things to try. > >Remi
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