Author: Robert Hyatt
Date: 13:22:51 06/25/98
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On June 25, 1998 at 15:01:54, Don Dailey wrote: >On June 25, 1998 at 09:43:45, Dan Homan wrote: > >>I'm not sure the right place to jump into this thread, >>but here will work... >> >>Is the speed-up from incremental move generation the >>only reason to use killers over the history heuristic? >> >>I've runs some quick 'n dirty tests on my program (which >>does not use incremental move generation... rather I >>generate all the moves at once and score them for sorting >>as I generate them), and the history heuristic by >>itself seems superior (in essentially all the positions I >>tested) to killers alone or killer+history. >> >>Perhaps my testing was flawed (it was very quick) or my >>implementation, but I was wondering if anyone else had >>a similar experience. >> >>For programs that do incremental move generation (like >>crafty), killers are surely a win because they don't >>need to do a full move generation if they get a cutoff. >>But what about programs that don't use this approach? >> >> - Dan > >My experience with history heuristic is a wash. My older >programs used to benefit a lot, but maybe too many move >ordering heuristics get in the way? I dutifully implement >this with each new program just looking for any small >advantage I can get and then always have to disable it. > >Are you saying history heuristic worked better when you >did not use the killers at all? > >- Don the two ideas are related... history moves are simply global killer moves. I like local killers as often they are better in a given position, but I also use history moves as this lets a great move farther out in the tree influence move ordering at nodes closer to the root, and vice-versa. In cray blitz, I tried lots of killer moves before giving up, not just the two at ply=N. I went to ply=1 or 2 , then 3 or 4 (depending on which side is on move here) and so forth. I took this out once and Harry screamed that we were way slower. But CB didn't use history moves. I didn't find history a big win, neither did it find it worse. It is good in places, does nothing in other places, but it is very cheap if you don't get into sorting the whole move list first... and if you give up after trying a few history moves, once you become convinced that you aren't going to fail high at all there.
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