2009/6/6 <dhillism...@netscape.net> > I think this is one of those design decisions that nobody takes on faith. > We all wind up testing it both ways and in various combinations. > > An additional advantage of using the number of visits is that branches at > the root become mathematically eliminated and can be pruned away. It often > also allows the search to be stopped early. It can save a lot of time for > forced moves.
Let me see if I understand what you are saying here. If you have set a goal time for thinking of 10 seconds, and let's say 6 seconds have progressed, then it might be possible to stop the search early if you do the math and see that it's not possible for any other move to have more visits given an additional 4 seconds? So when there is a position that has only a single clearly best move, perhaps a capture that cannot wait or a necessary atari defense, then you can probably save as much (or close to) as half the thinking time on that move. Is this correct? So if this understanding is correct, then it still makes sense to do the "pebbles" test at this point and check to see if another move has a higher score before stopping the search. If the move really is forced and necessary, then the answer will be no and you can stop early. If there is a move that currently appears better but with a "too small" sample, then it seems foolish to stop early. If the move is a result of just a few lucky playouts, then it will quickly be revealed and you can still stop early. - Don > - Dave Hillis > > > > -----Original Message----- > From: Michael Williams <michaelwilliam...@gmail.com> > To: computer-go <computer-go@computer-go.org> > Sent: Sat, 6 Jun 2009 5:07 pm > Subject: Re: [computer-go] Tweak to MCTS selection criterion > > Another strategy to be considered is to not allow the thinking to cease > until the maximum win rate and the maximum visit count agree on the same > move. Obviously this requires some extra code to make sure you don't lose on > time, etc. > > Brian Sheppard wrote: > > When a UCT search is completed, the usual selection criterion is > > "choose the move that has the most trials." This is more stable > > than choosing the move that has the highest percentage of wins, > > since it is possible to have an unreliably high percentage if the > > number of trials is small. > > > I have a small tweak to that criterion. Pebbles uses "choose the > > move that has the most wins." This rule selects the same move as > > the conventional criterion in almost every case. The reason why > > Pebbles' rule is superior is revealed in the case where the moves > > differ. > > > When Pebbles chooses a different move than the conventional criterion, > > it is because Pebbles move has more wins in fewer trials. When that > > happens, Pebbles move would inevitably become the move with the most > > trials if searching were to continue. So there is actually no downside. > > Of course, the upside is minor, too. > > > For validation, Pebbles has been using both strategies on CGOS games. > > At present, the conventional selection strategy has won 341/498 = > 68.47%. > > Pebbles strategy has won 415/583 = 71.18%. This isn't statistically > > conclusive or anything (0.7 standard deviations; we would need 4 to 8 > > times as many trials for strong statistical evidence). But Pebbles' > > strategy should be better by a small amount, and it has been, so I > > present it to you with confidence. > > > Best, > > Brian > > > _______________________________________________ > > 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/ > > ------------------------------ > Wanna slim down for summer? Go to America Takes it > Off<http://www.aolhealth.com/diet/weight-loss-program/?ncid=emlcntusheal00000001>to > learn how. > > _______________________________________________ > computer-go mailing list > computer-go@computer-go.org > http://www.computer-go.org/mailman/listinfo/computer-go/ >
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