On Wed, 2008-12-31 at 17:59 +0200, Berk Ozbozkurt wrote: > Heikki Levanto wrote: > > On Tue, Dec 30, 2008 at 08:01:27PM +0200, Berk Ozbozkurt wrote: > > > >> I think such a change may make engine objectively stronger while making > >> it more vulnerable against humans. Even if the human opponent isn't > >> aware of the move pruning logic initially, it wouldn't take a lot of > >> games to figure out that the computer never makes a move away from the > >> last move to the center or to the sides. > >> > > > > So sorry, but I think you have misunderstoodthe rule being tested here. It > > has nothing to do with the last move played, it is all about *not* playing > > to > > a point that is more than 3 (or 2) poitns away from any stone on the board, > > *or* that is on the 3th 4th, or the 5th row from the edge. > > > > This still leaves open a possibility of setting up two ladders, so that a > > ladder break somewhere in the center would be the right move. But even then, > > the random nature of the MC playouts would make such a position look pretty > > bad, and direct the program away from it - which would most often be good > > playing style anyway. > > > My real mistake was thinking this was a tree searching engine. My all > points are moot as this was only ref-bot doing AMAF. > > Assume, for argument's sake, the rule is implemented in a searching go > engine and moves not conforming to the rule are hard pruned during > search. It doesn't matter whether 2 points from any stone or just last > move is considered. In many openings neither side would have any stones > near the center, so no moves to the center would be considered by the > engine, for at least a few more branches down the tree. Note that, it is > the human opponent, who makes losing ladders with the intention of > putting a ladder breaker in the center. As the program is oblivious to > the fact that only one ladder may be won by it, the program will > evaluate its position *highly* and tend to continue ladders as long as > human continues playing them.
It is not necessary to construct an example - it's just understood that any imperfect rule can be taken advantage of. I think most game tree search expert understand that "hard pruning" is wrong in the sense that it produce non-scalable programs. It might make your program stronger in the short term as someone said, but you would now have some rule that a clever opponent can take advantage of such as the case you just constructed. No matter what hard pruning rule you come up with, someone can construct an example where it's wrong, unless of course the rule is 100 percent correct and fool-proof. You basically just set up a position where the opponent really must play the forbidden move knowing that he cannot see it. But that doesn't mean you should not use SOFT pruning or bias - even in the tree. In fact most progress in computer go and computer chess has been in shaping the tree using imperfect heuristics, sometimes domain specific. There is no convincing logic that I know of that says it's better NOT to do that. You can always construct an example of some position where it goes wrong, but go ahead and build a program with the principal of not using knowledge and I will show you an extremely weak program. The perfect example is humans. Full of contradiction, bias and imperfect knowledge. A clever enough player can take advantage of even the strongest human players with methods like you suggest. I think the key is that knowledge you add must be reasonable and practical. Generally, beginners are given good practical rules of thumb, that serve him well. But a good strong player following such rules religiously would be compromised. You see, the same rule can make one play much better, another much worse. The rule must be compatible with your competence. Image being able to construct hundreds of rules like the 3-4-5 rule that are applied in decision tree fashion. One can imagine the program playing better and better as you add more rules. At some point the program would reach a level of competence where you would have to reconsider some of the rules, because they are now hurting the program. The 3-4-5 rule might be good at first, but imagine (I know this is silly) that such a program reached several dan level. The 3-4-5 rule would have to be replaced, or refined with exceptions otherwise further progress is hindered. As a kid I did a paper program for chess that worked like this. You just followed the instructions and eventually a move was produced. The program was designed to delay development of the queen - because every beginner knows not to move your queen out early. So you could threaten the opponent in such a way that a queen move was required, and the "program" could not defend. But the program was so weak and primitive that it was still a good rule - i.e. better than no rule at all. - Don - Don > _______________________________________________ > computer-go mailing list > computer-go@computer-go.org > http://www.computer-go.org/mailman/listinfo/computer-go/ _______________________________________________ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
