AlphaGo and tengen

[moha]

It seems one could test the hypothesis that komi should be lower for weaker players by letting some weakish bots play each other a few zillion times with different komis, then examine the results.

I don't think SOME komi decrease could be doubted (for DDK levels at least), but the details are very vague. First, there is the "komi_ev" or "komi_wr" question. The two values that neutralize the EV (average board result) advantage or the winrate of the first player can differ somewhat, and the game can remain a bit unfair (either EV=0 or WR=50%, but not necessarily both). Also komi_ev is usually fractional, while komi_wr makes little sense in smaller than half point steps (so exactly 50% winrate cannot be expected anyway). Then there is the error distribution, IOW the kind of mistakes your weakish bots make - you may get slightly different results with different bots (or other groups of players).

One example is the token game above. With an odd number of tokens, consider two simple cases:
1. the players' error is that they sometimes pick a random token instead of the biggest one (with certain probability)
2. they sometimes pick the second-biggest instead of the biggest (with the given probability)

In the first case B's EV drop significantly (together with his winrate from 100%). But in the second case B's winrate drops but his EV increases, and both komi_ev and komi_wr will be higher than for perfect play.

[Bill Spight]

If small differences in komi had little to no effect in indicating proper komi for pros, they shouldn't make much difference for weaker players, either.

Bill, I'm not sure I follow. Are you saying that the small differences in komi had no effect on how the pros in the experiment played?

It was not an experiment. IIRC, they were data published by the Nihon Kiin.

If so, how did they determine that?

I observed that with the 4.5 komi games, if you subtracted 2 points from Black's point of view, making komi in effect 6.5, you got the closest to a 50-50 split. Subtracting 1 point from the 5.5 komi results also gave the closest to a 50-50 split. OC, that does not mean that a komi of 6.5 would give the closest split, because the players might play differently under that condition. I made that last point in a footnote to the article.

Additionally, I don't see how they could conclude that the correct komi should be 7 if all of the evidence is from games with komi of less than 7.

Well, the author of the article argued that since net go scores integers and the integer komi that would give the closest to a 50-50 split for the data was 7, that was obviously correct komi. IIRC, he was not arguing for a statistical split, but inferring that correct play would yield a result of 7.

Or is the upper bound inferred from other data -- such as the experience under Chinese rules?

No, he just used those 2800 Japanese pro game results. Actually, he has a better argument with Chinese scoring, because the vast majority of net scores are odd.

Much later edit: Corrected the number of games.

[luigi]

Would 7 komi be equally balanced if the button were used to break ties?

[Javaness2]

Petr Baudis already made such experiments over a variety of board sizes. I won't adjust your anticipation by mentioning where to see the results.

It is very exciting to me how fresh AlphaGo's play makes the game feel. So many times you see people just trotting out the same opening - they will continue to do so now with the additional option to imitate AlphaGo. Every time I see some insight from AlphaGo it beings new life into the game for me. However this 4-3 approach to 3-4 deserves an ear wigging.

[hyperpape]

In theory, we should get data, but I'm not doing that, so I'll add to the speculation. I won't be surprised if komi is smaller for dan level amateurs, SDKs or DDKs, but I won't be surprised if it's the same either.

Everyone seems to ignore the possibility that between certain sorts of weak players, komi is larger. Bill used the models of coupon-taking, but it only works if both players expect to take coupons of equal value on a given turn. Maybe weak players are prone to making unusually bad moves at some points as White.

Here's one way that could happen: in some kyu games, both players will sort of mindlessly build a large framework, but black tends to be a step ahead. Once that happens, it's an open question whether bad play leads to White invading and Black doing a bad job killing, or White playing passively and giving the game away.

Another fun variant: there are kyu players who immediately approach on move 2. They have a decent chance of coming away with sente and a decent position, so it's not always a loss, but once you're past the truly random level, you expect them to lose points on average.

[moha]

I'll add to the speculation. I won't be surprised if komi is smaller for dan level amateurs, SDKs or DDKs, but I won't be surprised if it's the same either.
Everyone seems to ignore the possibility that between certain sorts of weak players, komi is larger.

As I wrote earlier, I tried a few simple player-error models with the coupon game, and there indeed seems to be some cases where the komi is larger. But generally it is smaller OC, though I think not much smaller (since experienced human amateurs are closer to perfect play than to random play).