Rengo team effective rank?

I got to wondering if there is a likely effective rank calculation you could do for a two-person rengo team?

Are 2x 1k better or worse than 1x 1k?

Where would we expect a 1d + 10k to end up?

:face_with_monocle:


(admittedly, 2 person team rengo is remarkably rare at OGS, but hey … it still seems like an interesting question :slight_smile: )

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With no communication? Surely a team of two is worse than a team of one!

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This brings to mind an event from years back when Team Korea decisively outplayed Team China. It was revealed after the match that the Chinese professionals had rigorously debated each move, while on the Korean side, Park Junghwan had chosen all the moves, Choi Cheolhan checked them for errors, and the others were responsible for choosing lunch.

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I don’t think 1d + 10k (or even 9d + 10k) would be significantly stronger than 3k + 10k because the 1d has to play moves that the 10k can understand.

Definitely “with no communication”.

I would have thought almost for sure … although perhaps there is a "whoa, I would not have thought of that, but now I see it… " factor?

Interesting eh? And how much stronger than 10k would it be in either case?

I was about to guess 6k and 4k but I looked at the results of the European Pair Go championship 2021 and it appears that a 1d+15k pair defeated a 1k+1k pair… The strength of a pair probably depends a lot on whether the two partners know each other or not.

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Questions of communication between partners aside, maybe a scientific way of determining the rank of a pair is to use a bot to determine, for each rank r, the average number of points lost at each move L(r). Then, for a pair consisting of two players of ranks r and r’, the rank r’’ of the pair is the number such that L(r’‘)=(L(r)+L(r’))/2. So that r’’ is probably not the arithmetic mean of r and r’ since L is probably not a linear function.

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The formula we used at the London Open rengo to calculate team ranks for the handicaps was average of the ranks minus (number of players - 1).

And yes pairs/teams who know each other and play to each others strengths can make a huge difference.

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I’m talking about the situation of no communication between the team members.

IME the mean of the two team members’ levels gives a decent 1st order approximation of the level of the pair, if their playing styles match fairly well, the team members have experience playing pairgo and they are fairly well attuned to each other.

I think there is a good consensus that the level of individual players is mostly determined by their worst moves, so one might think that the level of a pair is mostly determined by the weaker member.

But an experienced weaker member can avoid some blunders by deliberately playing a ko threat elsewhere when they don’t know how to continue locally in a difficult fight, leaving the decision to the stronger member.
Also, an experienced stronger member who knows the weaker member well, may play into the weaker member’s strengths by steering more into a positional game (evaluation and building) or a more tactical game (reading and fighting).
Also, the weaker member may take a hint and abandon a local fight when the stronger member starts playing big moves elsewhere, signalling that a local fight has turned sour, or that there are little gains left in continueing that local fight.

Such pairgo tactics may not always work though. Sometimes the two weaker member of the opposing pairs tacitly decide to continue some local fight between the two of them, while the stronger members keep playing big moves elsewhere, unsuccessfully trying to persuade their weaker team members to abandon that fight. Then at some point one of the weaker members may make a mistake in that local fight, causing the stronger members to rejoin that fight to maximise the gains or to control the damage. These sort of things can lead to hilarious situations, which is part of the fun of pairgo.

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My gut feeling is geometric mean of the ratings

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How would a 9d get on if they were forced to pass every other move? I guess you’d need to allow them to respond to ko threats and take back kos and such.

But what I was wondering is how strong of a player could a 9d beat under such conditions.

And then my thought Is how weak of a partner would the 9d need to partner with for the pair of them to be the same strength?

(And then to get OT, would this tell us how strong you need to be before your moves are better than just passing?!)

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Off-topic, but I like to bring up this example from Denis Feldmann’s bestiary every chance I get:


Suppose we start from this position. Black plays first, but white gets two moves after every black move. Can black win?

Solution

Nope! In fact, the black group is dead. It does not take much effort for white to deny black even a single eye:

That should give some idea about how brutal the “pass every other move” handicap is!

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Once i played a rengo against A. Moussa (french champion multiple times), he was paired with a very weak player. So i tried to skip his move at a crucial time, he went a bit furious and tenukied my threat. And we lost (in shame for me…)

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