Swiss System Tournaments Ending Early

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turtler7
Posts: 147
Joined: 23 December 2016, 00:01

Swiss System Tournaments Ending Early

Post by turtler7 »

https://en.boardgamearena.com/#!tournament?id=11471
In this tournament I won both the first matchups securing a guaranteed 1st place for such a low player count. Rather than having tomorrows matchup let the other two players face each other to compete for 2nd vs 3rd, the tournament instantly concluded. Since the tie breaker is the standing of opponent they faced (same person so tied again) and then the elo of that opponent (I had won in the first day so my elo was higher in the second game played) the person who was randomly selected to go second (I believe the lowest elo player in the registration) gets the 2nd place win over the player who went against me first.

This is not the first time I have seen a swiss system end prematurely when 1st place was undefeated and all other places had at least one loss even if several matches remained. There were enough remaining matches for the 1st place to be upset by the 2nd had the matches gone the right ways or at the very least 2nd and 3rd place titles were still up for shuffling among several different players who had a chance for it.
https://en.boardgamearena.com/#!tournament?id=11464
That one for example ended 2 games before the end with a swiss system 7 round with 8 players (I thought it was going to behave exactly like a round robin for that final player count).

I have not yet done any research into the traditional swiss system algorithms and apologize if they always prioritize the earliest they can call a 1st place victor regardless of what the rest of standings look like or how many planned games remain. If anyone can point me towards documentation on how to study the swiss format decision matrix that would be a much appreciated (level of math complexity is no issue to me).
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kingneal
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Joined: 27 May 2017, 21:21

Re: Swiss System Tournaments Ending Early

Post by kingneal »

Swiss tournaments by definition play until a winner is determined (last undefeated).
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turtler7
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Re: Swiss System Tournaments Ending Early

Post by turtler7 »

kingneal wrote:Swiss tournaments by definition play until a winner is determined (last undefeated).
That does not seem true or is at the least incredibly inconsistent. If you check that second link it did not end when one player was undefeated. With 8 players 4 are undefeated first round 2 the 2nd and 1 left in the 3rd round. Both undefeated dueled in the third round and a winner was decided. But then the game played a 4th and a 5th round as scheduled but not the 6th and 7th as scheduled (it would have reverted to round robin)

https://en.boardgamearena.com/#!tournament?id=12798
Here is another example of a tournament having one undefeated player left in round 4 and continuing to round 5.
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kingneal
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Re: Swiss System Tournaments Ending Early

Post by kingneal »

my mistake....did some research and swiss is meant to be a set number of rounds with the top facing the top each round when possible.

My history is starting through cases system where they had a swiss and what they called a "true swiss"....swiss ended when there was one undefeated left and a "true swiss" was a full round robin. I have now found that neither of them were an actual swiss. Swiss was originally designed for larger leagues where a full round robin would not be feasible and are actually designed to go a certain amount of rounds regardless.
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sprockitz
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Joined: 23 October 2014, 02:22

Re: Swiss System Tournaments Ending Early

Post by sprockitz »

Swiss tournaments will end if there are no possible matchups to make. This can frequently happen with 2 rounds remaining because each round is scheduled without concern for making future rounds possible (and a swiss is restricted to not playing the same person twice).

In the 8 player example above you have a group of 3 players who haven’t played each other, which makes scheduling a 6th round impossible...therefore the tournament is ended.

I’m not sure about the 3 player tournament, seems that might have been an issue long ago that has since been corrected as I haven’t seen any issues with it.
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Robo65
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Re: Swiss System Tournaments Ending Early

Post by Robo65 »

In the linked 3-player tournament, every player played 2 games. This is the most that can be done. Even if you play round robin, there will only be 2 games for each player. So there's no bug.

The idea of a swiss tournament is to be a better KO System. In KO, you can have 2^K players in K rounds (e.g. 3 rounds for 8 players), but one half of the players become bored spectators after each round. The swiss system requires as many rounds as KO, but all players stay in the game until the end. After round 1, the top half of the players are only winners. After round 2, the top quarter, and so on. After round K, there should be exactly one player at the top who has won all of their games, as in KO. This may not be the case if you don't have exactly 2^K players, but then the Buchholz evaluation comes as the tie breaker.

Of course you are free to add extra rounds to a swiss tournament, as long as there are possible matches for everyone. If you're lucky, you can continue until you went full round robin. But then, Buchholz makes no sense any more, because everyone has played against everybody else, and you need a different tie breaker.

Robo
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Espina
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Re: Swiss System Tournaments Ending Early

Post by Espina »

Robo65 wrote: 08 December 2019, 14:20 In the linked 3-player tournament, every player played 2 games. This is the most that can be done. Even if you play round robin, there will only be 2 games for each player. So there's no bug.


Robo
Actually, if you look carefully, only turtler actually played two games. Each of the other players got a "by" in one of the rounds (meaning they "won" by default because of being matched against a non-existent player.)
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Robo65
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Re: Swiss System Tournaments Ending Early

Post by Robo65 »

Yeah, you're right, please excuse my mistake. But I don't know if you can handle that correctly by the principles of a swiss tournament. Because matches are made from top to bottom, and if the number of players is odd, then the last one in the list can't play.

To invent a new principle, let assume that there are N=2K+1 participants and the tournament needs more rounds to fulfill the minimum number of rounds (ceil(log2(N)). Then, if BGA can't match 2K players by giving a free ticket to player N, maybe they should retry with Player (N-1), then (N-2), down to player 1, until success or until no match is possible. In this tournament, it would have worked.

Don't know if that's a generally good idea, and the question is: does anybody else do this? What are the consequences for fair ranking? For Buchholz Numbers? According to Wikipedia, swiss tournaments where you must abort because you can't match anymore do happen, but usually not in one of the mandatory rounds.

The conclusion could be: size matters. A swiss tournament with less than 4 players (2 rounds) makes so sense. BGA could switch those tournaments to 3 rounds of round robin automatically, or refuse to start and give an option to change the tournament mode to round robin. In my eyes, the minimum for swiss could actually be 8.

Robo
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