McMahon Pairing
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(WME Ongoing)
McMahon Pairing is a subset of Swiss Pairing which has become the standard choice for amateur tournaments in Europe and America.
Explanation
Where McMahon differs from Swiss is in the initial starting scores. The players begin with a Score determined by the rank at which they entered. So for instance, a 5kyu would begin at 2 points higher than a 7kyu. The important exceptions are introduced by the bar, upper or lower.
- Above the (upper) bar are placed all those deemed to have a reasonable shot at winning the tournament. So if the bar is at 5dan, then a 7dan a 6dan and a 5dan would start on the same score, all 1 point above a 4dan beneath the bar.
- A lower bar is not always included, but beneath this we treat all players to be the same rank. If the lower bar is 19kyu, then a 35kyu and a 20kyu would start at the same score.
Now the tournament director attempts to pair players with similiar scores together using one of the methods specified in tournament pairing or, perhaps, another method. Everyone who wins a game gets 1 point, losers 0 points, and jigo 1/2 a point, added to their score. We call the score, perhaps unsuprisingly, the McMahon Score or MMS. Byes are normally awarded a half point, but this is not always the case.
History
The system is named after Lee McMahon of New York Go Club, but it was spirited out of NY into Britain where it (eventually) found its current form.
Tim Hunt writes...
"The remarkable thing about the history of the McMahon system is that such a successful tournament system arose as the result of a transatlantic misunderstanding. According to Francis Roads (revered BGA member) who was there at the time, this is what happened:
The first three British Go Congresses (1968, 1969 and 1970) were run as handicap, or open + handicap tournaments. Then for the 4th (1971) BGC they tried the McMahon system, because they wanted a system where most games were approximately even games, but where everyone was really playing in the same tournament, rather than being split up into different classes. The McMahon system they used was loosely based on and named after the McMahon system used by the New York Go Club. What the British did not realise was that the New York system was, in fact, a club ladder/grading system, not a tournament system. Anyway, the BGA used it as a tournament system and, apart from one small bug (later) the first time around, it seemed a success. So much so that eventually it spread to Europe and back to America.
The bug: the mistake they made the first time around was to say if you win you move up one, and if you lose you go down one (rather than staying the same). This meant that if your McMahon score was even in the first round then it was odd in the second round and vice-versa and similarly in later rounds. This meant that people who started with an even McMahon score (almost) never played people with an odd McMahon score and so effectively they had two separate tournaments going on side-by-side. Oops! They got it right the second time around."
It is often called MacMahon too, but nobody is quite sure why. The BGA Journal Feb 1978 refers only to MacMahon for example. Although a few years previous to that, McMahon was exclusively mentioned.
Usage,Software etc
The exact operation of the McMahon tournament can be rather varied. Depending on which program you use to direct your tournament (if indeed you use one!) there can be significant differences. Lower bars may vanish, the population above the bar can change, same club pairings may be forbidden, handicap treatment can vary too.
You will find more details at Tournament Directing Software but the main programs are
- EPM - Finland
- GoDraw - UK
- Gotha - France
- MacMahon - Germany
- MacTD - US
References
There is a hodgepodge of other information available on the topic.
Here are some pointers to further explanations of the system:
-
Christoph Gerlach's thesis (PDF file, in German)
-
Cambridge Go club page on McMahon
-
Geoff Kaniuk on McMahon
-
Olli Lounela's description of McMahon (
Wayback machine link (2002) to Olli Lounela's page )
-
McMahon explained in German language (by Christoph Gerlach)
- According to page 95 of the 1986 Ranka Yearbook (at least as quoted
here), the original McMahon system was invented by Lee McMahon and Bob Ryder of Bell Labs.
Personally I would be interested in finding more information on the original usage in New York Go Club.
See Also: Tournament Pairing, Swiss Pairing.
Examples
Variants
- Aguilar-McMahon
Migeru: The 2005 Iberoamerican Go Tournament is being run (on KGS) by dividing the participants into 4 groups initially:
7d- 1d -- 3 McMahon points -- 14 players 1k- 6k -- 2 McMahon points -- 44 players 7k-13k -- 1 McMahon point -- 43 players 14k-20k -- 0 McMahon points -- 37 players
This was actually on the suggestion of Fernando Aguilar who thought this addressed a number of concerns that players had been expressing over the years, and the results of trying out different variations of the Swiss/McMahon system. The tournament will last 8 rounds.
What was the general opinion as to the success of this format?
Phelan: I can't be sure now, but from what I remember it was favorable. The biggest problem was higher level players not playing some rounds. Some lower level players were ranked below them, despite playing all games in the tournament. Results at
http://www.goprat.es/TIG2005.TXT