Talk:Round-robin (sports)
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[edit] Creating
I replaced the following section because I find it hard to follow. My version is not as pretty, but I reckon it makes sense. It's based on the last post here: Mon, 03 Nov 1997 16:39:06. Joestynes
- A pure round robin grid requires
games, where n is the number of teams in the tournament. In many cases (e.g. football), 
games can be run in parallel.
- To create a round robin grid, break it conceptually into a number of rounds. In the first round, each participant plays the participants immediately above and below them in the list of teams. In the second round, each participant plays the participants two spots above and below them; and so on for subsequent rounds. If there are an even number of teams, it will be necessary to finish with a half-length round, in which each team plays the team spots above/below them. A sample for 6 teams is shown below.
- Each row in this grid is a participant, and each column is a game. For example, looking at the first column, we can see that in the first game team A plays team B. The colors represent whatever is appropriate for your sport: red is home and green is away; upwind and downwind; left end and right end, etc.
- Each participant plays twice in each round (except the final half-length round, if there is one). Each participant is red once and green once in each round (except in the half-length).
- You can scale this to any number of teams, in a way which hopefully is obvious from the example. You can rearrange games to suit; in particular in some sports you will want to rearrange so that no participant plays twice in a row. In any given round, the games can be arranged into two groups which can be run in parallel; for example in the first round above, games 1, 3 and 5 can be run in parallel, as can games 2, 4 and 6.
[edit] Replaced with
The standard algorithm for round-robins is to assign each competitor a number, and pair them off in the first round …
1. (1 plays 14, 2 plays 13, ... ) 1 2 3 4 5 6 7 14 13 12 11 10 9 8
… then fix one competitor (number one in this example) and rotate the others clockwise …
2. (1 plays 13, 14 plays 12, ... ) 1 14 2 3 4 5 6 13 12 11 10 9 8 7
3. (1 plays 12, 13 plays 11, ... ) 1 13 14 2 3 4 5 12 11 10 9 8 7 6
… until you end up almost back at the initial position
13. (1 plays 2, 3 plays 14, ... ) 1 3 4 5 6 7 8 2 14 13 12 11 10 9
If there are an odd number of competitors, a dummy competitor can be added, whose scheduled opponent in a given round does not play. The upper and lower rows can indicate home/away in sports, white/black in chess, etc (this must alternate between rounds since competitor 1 is always on the first row). If, say, competitors 3 and 8 were unable to fulfill their fixture in the third round, it would need to be rescheduled outside the other rounds, since both competitors would already be facing other opponents in those rounds. More complex scheduling constraints may require more complex algorithms.
Hi, Joe. If you reckon yours is clearer, I'm happy to leave it up. What do you think about adding back in the initial paragraph from my version about the number of games required? DougBurbidge
- Yep: done, more or less. Proofreading and maths-checking encouraged. Joestynes 10:06, 11 Apr 2005 (UTC) [P.S. name's Jöstij, actually :)]
Hey, sorry about my etiquette, but I just wanted to mention that something seems to be wrong here.
For 8 participants …
8/2(8-1)=28
1 2-3-4-| / | (1) 8-7-6-5-|
1 8-2-3-| / | (2) 7-6-5-4-|
1 7-8-2-| / | (3) 6-5-4-3-|
1 6-7-8-| / | (4) 5-4-3-2-|
1 5-6-7-| / | (5) 4-3-2-8-|
1 4-5-6-| / | (6) 3-2-8-7-|
1 3-4-5-| / | (7) 2-8-7-6-|
I just realized in composing this that the total number of matches would be 28, but it wasn't apparent to me at first however. I don't know if it needs clarification or not it could just be me being stupid. Perhaps it could be said the total number of rounds or least possible amount of rounds, assuming the most possible matches per round played, would be n-1?
- The least possible amount of rounds is n-1 if n is even, and n if n is odd. This is already stated in the article:
- If n is even, then in each of (n − 1) rounds,
games can be run in parallel, provided there exist sufficient resources (e.g. courts for a tennis tournament). If n is odd, there will be n rounds with 
games, and one competitor having no game in that round.
- If n is even, then in each of (n − 1) rounds,
- Joestynes 16:54, 10 January 2006 (UTC)
[edit] Proposed move to Round-robin tournament
That was a short American-centric article with no edit history talk page. I incorporated its extra information to this article and redirected it here. Just need an administrator to rename. Joestynes 11:43, 6 Apr 2005 (UTC)
- Support move. Round-robin tournament will be easier to link to in running text. It's also a better title because the concept is not just in sports. It's used in table games, such as chess tournaments, for example. Jonathunder 01:18, 2005 Apr 7 (UTC)
- Support move, but I think we should merge the histories, and not leave a redirect at Round-robin (sports). We can edit the pages to point to the correct title. -- Netoholic @ 01:32, 2005 Apr 7 (UTC)
- Since the concept is used in other venues besides just sports, I support the move, and yes, we can eliminate the redirect too. -- TOttenville8 07:31, 2005 Apr 7 (UTC)
- Support. Even though most of the material I added has been cut out again. :-) DougBurbidge 07:16, 10 Apr 2005 (UTC)
It was requested that this article be renamed but there was no consensus for it be moved. This is a page merge not a move. I do agree, though, that round-robin tournament is a better name. violet/riga (t) 11:14, 10 Apr 2005 (UTC)
- I have overwritten the old content of Round-robin tournament with the old content of Round-robin (sports) and made the latter a redirect; the talk page now redirects in the opposite direction. I had already done my best to merge the content prior to the rejection of the move request. Not sure if this is procedurally kosher but nothing's been happening about clearing up the duplicacy. Joestynes 08:10, 25 May 2005 (UTC)
