Author: Larry Griffiths
Date: 19:36:26 08/28/00
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On August 28, 2000 at 22:21:40, Robert Hyatt wrote: >On August 28, 2000 at 19:32:05, Larry Griffiths wrote: > >>I have been reading about the History Heuristic and have seen pro's and con's >>about it. >> >>I plan on implementing it to see what happens. This heuristic is related to >>killer moves and uses the from and to squares in a 64 x 64 array to maintain >>history information when moves are bestmoves or cutoffs. Each entry has 2 to >>the depth power added to it when a bestmove or cutoff is found. >> >>Would you recommend the History Heuristic, and has anything changed for the >>better with the method described above? >> >>Thanks in advance. >> >>Larry. > > >Works fine, but don't use 2^depth... for reasonable search depths, that will >overflow 32 bit counters almost immediately. I use depth^2 which is much >safer... > >Other than that it works fine. If you don't get a cutoff by the time you have >tried a few history-ordered moves, you probably should give up and just search >the rest of the moves in random order. I have Jonathan Schaeffer's paper "The History Heuristic and Alpha-Beta Search Enhancements in Practice". I also figured the counters might overflow and it looks like he ran his tests to around 9 plys. He also describes that the history tables can become flooded with information, decreasing their usefulness. I wondered if this was due to an overflow of his counters at plys 8 and 9. Excuse me Bob, but I have not done powers in quite a while and I was thinking 2^depth amounted to shifting the binary value 2 left depth positions. Maybe I am just tired, but is depth^2 like depth squared? I plan on using 64 bit counters so I am not worried about overflowing the counters. I thought I would also try different formula's for calculating the weights. Larry.
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