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
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