Author: Andreas Stabel
Date: 08:27:14 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. There is perhaps an in between solution. Not to put moves already done into the hash table, so only positions encountered twice in the same path in the actual search is counted as a draw. Of course this has to go together with a check in the root if any of the legal moves leads to a third repeat. The problem above is very visible when I analyze a match between two GMs, and one has a big advantage, tries a move which gives to other the chance to go back to a previous position, and now crafty thinks it is a draw ! Regards Andreas Stabel
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