Author: Peter McKenzie
Date: 20:45:47 10/07/99
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On October 07, 1999 at 21:21:39, Robert Hyatt wrote: >On October 07, 1999 at 20:45:08, James Robertson wrote: > >>My search currently decides a position is drawn if it has repeated twice. I >>think this is causing my search to sometimes stuff 2nd rep draw values into the >>hash table that can be retrieved for positions with different history's. Is this >>a problem? What do other people do? Could I just not store any draw values in >>the hash table? Should I go to draw by 3rd rep? >> >>Thanks, >>James > > >Dave Slate used to advocate not storing draws in hash table. Ken Thompson >and I both did (and I still do). Either way has its drawbacks... What you (James) are doing is fine. Not hashing draws doesn't actually solve the problem it is trying to solve. The main draw back with hashing draws after the 2nd rep is that sometimes you have a really bad position and have the opportunity to either: a) make a move that will repeat a position for the 2nd time or b) make a different move that will improve your position but still leave you with a slightly negative score Your program will choose to repeat for a 2nd time, thinking the score is zero. But your opponent might then play a crushing move that gives you a large negative score. The program would have been better off not repeating, and instead improving its position. A partial solution to this is to be extra careful with how you recognise draws by repetition when near the root. Ie. only score a node as drawn if it has actually repeated 3 times in the tree. cheers, Peter
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