Author: Uri Blass
Date: 02:12:32 07/18/01
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On July 18, 2001 at 01:37:56, Artem Pyatakov wrote: >I am not sure if Dr. Hyatt is back yet, so if someone else can answer this I >would appreciate it. > >I was looking at the way Crafty handles repetition and came across the following >comment: >/* > ---------------------------------------------------------- >| | >| insert the board into the next slot in the repetition | >| list. then scan the list. we look for the case where | >| the position has been seen one time before, unless we | >| are at ply 1 or 2, where we must have seen the same | >| position twice prior to this. | >| | > ---------------------------------------------------------- >*/ > >There is also a related comment: >"note that for a repetition to happen in the first two plies of the tree, the >position has to be repeated three times, while for plies beyond two, two >repetitions trigger a draw score." > >My question is this: Why does Crafty make this exception for plies 1 and 2? What >is special about them? > >Thank you. Suppose that your program blundered in the last move and repetition of previous positions is now the only way to win the game. If your program evaluates repetition in the first 2 plies as a draw it may avoid the repetition and choose another option that leads to a draw. If your program does not evaluate repetition as a draw in the first 2 plies it may repeat and win the game. I guess that evaluating second repetition not in the first 2 plies as a draw is done because not evaluating it as a draw can cause other problems(the program may be significantly slower) Uri
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