Author: Bruce Moreland
Date: 00:06:56 10/08/99
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On October 07, 1999 at 23:45:47, Peter McKenzie wrote: >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. This has to be too conservative. I think there are two better choices. 1) Score a position as drawn if it has happened either in the game continuation or somewhere directly above in the search tree. 2) Score a position as drawn if it has happened twice in the game continuation and/or once somewhere directly above in the search tree. The first method is the classic way of dealing with this. Basically any sort of repetition is scored as a draw. The second method tries to address the problem wherein you'll play back into a lost game if the opponent had a win, missed it, and is still either drawn or slightly better. Here is an example. In a very early game my program was down two pawns. The opponent made a reversible move that was a blunder. My program made a reversible move that won a pawn. The opponent realized he had made a mistake and reversed his previous move, since that was the best defense. My program could have taken the pawn, leading to a position where it was a pawn down, but instead it reversed its move, thinking that this was a draw, but actually it allowed the opponent to avoid the blunder and remain two pawns up. The drawback to the second method is that you get a lot of repetitions in actual games, which can lead to enraged opponents and possibly some 50-move draws in endings where the program would be forced to make progress otherwise. bruce
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