How are initial McMahon scores calculated? Probably a bug


#1

This is how I think, how McMahon score is calculated (based on https://senseis.xmp.net/?McMahonPairing):
The initial score depends on your overall rank. Every player above the McMahon bars starts with 0 points. The score within the McMahon bars is reduced for weaker players (lower rating, fewer starting points). Below McMahon bars every player gets the lowest points.

In the just started Tianyuan Nines Title Tournament, the initial score near the McMahon bars looks a little random to me. The McMahon bars are (9k-3k). For example there is a 2k player with initial rating of -4, a 7k with -2 and a 4k with 0 points.

Therefor I’m wondering, how OGS calculates the initial score.



Edit: The screenshots were made before the points where adjusted to fit the special Tianyuan initial points. Therefor the screenshots should show the points as calculated by the OGS system.

The pairing seems to be off as well. It is set to Strength but player of similar strength are scattered over multiple groups.


Tournament Pairing Method Strength doesn't work as expected
#2

If I remember well this isn’t the first time someone asks for this.
I can’t find any answer in the forum though.


#3

There’s this:
https://senseis.xmp.net/?OGS%2FTournamentFormats


#4

It says:

All groups will be sorted into groups of 5 players, seeded but with players of the same ability directly together (top 5 players in the top group, next 5 players in the next etc).
All players in the top group will start at 0 points, in each group below will start with 1 less point (-1 for the second group, -2 for the third group etc).

In the tournament above there are 27 players that started with 0 points.
9 players with -1 points
18 at -3
9 at -2
36 at -4
9 at -5 and
7 more at -4 (the last group?.. but why at -4? )

The only pattern I see is that each group is made of players with the same initial score.
There are 9k at -2 and also at -4.
Pairing should be strenght, but dans are not together.
I’m quite confused.

Is it possible that pairing uses an old rating? Perhaps the one at the moment of subscription…


#5

Thank you for providing the link. The initial points were adjusted accordingly after I wrote this post.

My original question was more directed at how OGS calculate initial McMahon points in general. Since the points got adjusted after I created this post, I would infer that this are the scores OGS calculated automatically.


Your link rises an other question:

The page you linked states

All groups will be sorted into groups of 5 players, seeded but with players of the same ability directly together (top 5 players in the top group, next 5 players in the next etc).

substituting "same ability with “same rank” I would expect that the players should be sorted according to their rank. But it looks like players of similar rating are spread over many different groups.

Is this an error in sensais?


#6

That was my guess when I had been wondering about the same a while ago.


#7

Changed category and title to indicate that this could be a bug.