Author: Bruce Moreland
Date: 13:37:41 01/20/99
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On January 20, 1999 at 12:01:14, KarinsDad wrote: >On January 20, 1999 at 10:08:15, Robert Hyatt wrote: > >>On January 19, 1999 at 20:20:48, Larry Griffiths wrote: >> >>>I ran my program with Alpha-Beta and without Alpha-beta. >>>The scores and moves chosen were different. >>> >>>Is this normal for Alpha-Beta or is this an indication of an >>>error in my implementation of Alpha-Beta pruning? >>> >> >>It's a bug. Alpha/beta _must_ produce the exact same result as minimax, >>this was proven in "An analysis of Alpha/Beta Pruning" written by Knuth and >>Moore, 1975.... > >Actually, it is not necessarily true that there is a bug in the code. There is >an assumption on that. Since the min max search should have been exhaustive to a >certain depth, you cannot run the program to a deeper depth with the alpha beta >or the scores could change which in turn could result in different moves as >well. > >If the alpha beta was able to search deeper than the min max, then there is a >bug in the testing as opposed to a bug in the code. I think the assumption is that he's running to the same depth, otherwise of course it won't return the same score and PV, otherwise we'd all search to depth = 1 and quit. bruce
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