Author: Bruce Moreland
Date: 13:35:31 01/20/99
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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? > > > >Also, The time is 1052.58 seconds without Alpha-Beta >and 3.3 seconds with Alpha-Beta. > >What ratio of elapsed time would indicate that I have achieved >good move ordering etc. with the Alpha-Beta pruning? You should get the same score unless: 1) You have a hash table that you use to prune, and do any path-dependent scoring such as 50-move rule, or repetition detection. 2) You do forward pruning based upon alpha or beta. This includes null move forward pruning. 3) You do any sort of imperfect hashing such as pawn structure hashing, where it might be possible that two pawn structures could have the same hash key, and this might go undetected. You should get the same variation (and same score) returned unless: 1) You do any of the above. 2) Your move ordering system has anything to do with positions seen previously, for example history heuristic and possibly killer move heuristic. You should be able to take the "if (score >= beta) return score;" line out of your program and have it return the same scores and same PV's, in signficantly longer time, unless you do any of the above, or you have a bug. bruce
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