Author: martin fierz
Date: 00:36:50 06/30/03
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On June 30, 2003 at 03:09:08, Christophe Theron wrote: >On June 29, 2003 at 10:29:33, martin fierz wrote: > >>On June 28, 2003 at 11:20:21, Frederic Louguet wrote: >> >>>I read an interesting paper from Albert Xin Jiang and Michael Buro about >>>Multi-ProbCut and its implementation in Crafty. I have always been very >>>skeptical about this pruning technique (for chess) but the paper is rather >>>optimistic. However, the data presented does not seem very convincing from a >>>statistical point of view (too few games, not enough opponents). So could Robert >>>Hyatt tell us a little more about the effectiveness of this technique ? Does it >>>_really_ work ? >> >>i can't really tell you anything about chess, but i tried multi-probcut (MPC) in >>my checkers program. the general opinion about checkers is that null-move is not >>a good idea there, so everybody uses his own hand-crafted pruning algorithm. >>therefore, MPC seemed like an interesting candidate for my program. MPC >>performed much better than no pruning, but also clearly worse than my (highly >>checkers-specific) own pruning. i ran matches with 300 games/match, so the >>results were statistically significant (i don't remember the numbers off-head). >>i don't see why MPC shouldn't work in chess if it works in other games like >>othello and checkers. whether it's better or worse than nullmove i have no idea. >>as a general observation, i find it hard to believe that any generic pruning >>algorithm (like MPC & nullmove are) could perform better than one which >>incorporates game-specific knowledge. > > > >The fact that a pruning algorithm works in a certain game tells you that >obviously this algorithms incorporates game-specific knowledge. > >In particular, the fact that null move works well in chess tells you a lot about >the essence of this game. At least it gives you an important information about >the game. > >By searching, and finding, good pruning algorithms for a given game we improve >our knowledge of that game. The fact that a pruning algorithm works reveals >something about the game that maybe you did not know before. > > Christophe let me try to reformulate what i meant: a pruning algorithm that knows something about the specific game should do better than a generic pruning algorithm, always. things like nullmove and MPC are very generic, i.e. you can add them to any game-playing program in more or less no time at all, and the program will usually improve. don't get me wrong, i like the concept of MPC very much, exactly because it's game-independent. when you say that null move works well in chess, you are talking about "normal" positions; in zugzwang situations it fails. AFAIK chess programmers have some defenses when not to use null move (or to use some double null move or something - i know too little about what you guys are doing...). this is what i meant: adding some game-specific knowledge improves the generic pruning algorithm. with MPC it's similar: although it's generic, it includes some game-specific knowledge in the form of the coefficients used, which are the correlation between scores at different search depth, which is then game-specific. this makes MPC adaptable to any game. in my experience, there are two problems with MPC: 1) it generates horizon effects in the search tree in it's shallow searches, which i avoid with my own pruning scheme. 2) it has no game-specific knowledge on when not to prune included. cheers martin
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