Author: Bruce Moreland
Date: 09:12:07 03/08/00
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On March 08, 2000 at 08:34:45, Robert Hyatt wrote: >On March 08, 2000 at 05:11:11, Howard Exner wrote: > >>Test your chess engine if it handles this repition theme correctly. To do this >>set up the position below and play the white side yourself. Do not enter the >>winning move Kh5 but instead play the blunder Kg5. Now let your program play the >>black side at say game/15. It will of course play Kd5+ which forces perpetual >>check. After it does that try to trick the program and reply Kg4. >>Now the test - does your program play the correct Qd1+ or does it blunder and >>mistakenly repeat the position with Qe4+, assuming that the opponent will >>blunder again with Kg5? Rebel Century failed this test and assumed white would >>play again the poor move Kg5. >>Why would a program do this? Do other programs fall into this trap of assuming >>a repetition of moves even when not forced? >> >>[D]8/4k3/7Q/8/4q1KP/6P1/8/8 w - - > >This is a known problem. Most count 2-fold repetition as draw, as if the >2-fold repetition can be forced with best play, the 3-fold repetition can also >be forced. In this case it is wrong, but generally it works fine. > >fixing this is easy, but the fix is far worse than the problem. Because to >require the search to see a 3-fold repetition to recognize a draw would make >most draws too deep to see. I've been explaining for years how to fix this. Any 2x rep in the search is counted as a draw, and any 2x rep in the game history, plus one rep in the search, is also a draw. The only case that is now considered a draw, which would not be considered a draw under this system, is one rep in search plus one rep in game history. That's no longer a draw. The benefit is that you never have to worry about this very stupid problem again. The drawbacks are: 1) You may not allow someone who is beating you to take a repetition. 2) You may play into repetitions yourself, which annoys your opponent and in some cases may cause you to draw games via the 50-move rule. This is actually fairly serious, and I still use the old method for very low material endgames such as KBN vs K, if I'm not using tables. bruce
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