Swiss Pairing Minimum Numbers?

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Roger de Coverly
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Re: Swiss Pairing Minimum Numbers?

Post by Roger de Coverly » Thu May 26, 2022 5:38 pm

Francis Fields wrote:
Thu May 26, 2022 5:12 pm
The point of the Swiss pairing system ( as believed to be devised by Arpad Elo ) is to aim to pair players of similar strength.
I thought it was to establish a winner when there are more players than could be accommodated by an all play all and for more games to take place than there would be in a knock out.

The earliest use of Swiss pairings would predate the establishment of rating and grading systems. Indeed for many years it was the practice to pair randomly after establishing score groups and colour sequences.

The British Championship of 1949 invited more players than an all play all would accommodate and used Swiss pairings. There are presumably earlier examples.

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Matt Mackenzie
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Re: Swiss Pairing Minimum Numbers?

Post by Matt Mackenzie » Thu May 26, 2022 6:24 pm

Surely its main purpose is to "pair people with similar *scores*" which may or may not strongly correlate with playing strength.
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Re: Swiss Pairing Minimum Numbers?

Post by JustinHorton » Thu May 26, 2022 7:06 pm

Francis Fields wrote:
Thu May 26, 2022 5:12 pm
The point of the Swiss pairing system ( as believed to be devised by Arpad Elo)
No
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John Upham
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Re: Swiss Pairing Minimum Numbers?

Post by John Upham » Thu May 26, 2022 7:07 pm

Francis Fields wrote:
Thu May 26, 2022 5:12 pm
The point of the Swiss pairing system ( as believed to be devised by Arpad Elo ) is to aim to pair players of similar strength. This requires more players than a theoretical minimum.
Incorrect on the first point:
The system was first employed at a chess tournament in Zurich in 1895 by Julius Müller,[2] hence the name "Swiss system",[1] and is now used in many games including chess,[1] go,[3][4][5] bridge and Scrabble.
Your second point makes zero sense but then again, DS did warn me not to engage!
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SeanCoffey
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Re: Swiss Pairing Minimum Numbers?

Post by SeanCoffey » Thu May 26, 2022 7:49 pm

Pairings are always possible (ignoring, as always, colour restrictions) if the number of players is at least twice the number of rounds.

(This is part of Lemma 2.1 in the second reference I gave above.)

One comment above was that when the number of players is small, it might be useful to check when pairing one round that that pairing allows the following round to be paired. One fact I found, which I thought was not obvious at all, is that even this might be enough. I.e., it's possible that a problem will inevitably arise two rounds from now, even if the current round can be paired. There is a known example with 10 players--bad pairing in round 6 allows multiple pairings in round 7, but none in round 8--among other examples.

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Re: Swiss Pairing Minimum Numbers?

Post by Francis Fields » Sat May 28, 2022 11:38 am

Do people accept that a 'formula' like the Swiss pairing system is better than random pairings?
It then follows that the accuracy as governed by the number of players should be considered.

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John Upham
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Re: Swiss Pairing Minimum Numbers?

Post by John Upham » Sat May 28, 2022 12:37 pm

Francis Fields wrote:
Sat May 28, 2022 11:38 am
Do people accept that a 'formula' like the Swiss pairing system is better than random pairings?
Yes

Francis Fields wrote:
Sat May 28, 2022 11:38 am
It then follows that the accuracy as governed by the number of players should be considered.
It does not follow. Let us say that more than half of the players are unrated for example.

Are you attempting to postulate that the more rated players in the draw make the pairings for that round more "accurate"?

(I'm not sure why I am bothering with this: I guess it amuses me).
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Roger de Coverly
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Re: Swiss Pairing Minimum Numbers?

Post by Roger de Coverly » Sat May 28, 2022 12:38 pm

Francis Fields wrote:
Sat May 28, 2022 11:38 am
Do people accept that a 'formula' like the Swiss pairing system is better than random pairings?
Underlying premises of a Swiss system are to pair people on the same score group and not to pair the same players more than once. Within score groups there are various methods of deciding who plays who, one of which is by random pairing. With the development of software to do the legwork, more detailed rules have been developed.

Various people have attempted pairing methods which would pair people of similar ratings rather than similar scores. They didn't catch on other than accelerated pairing methods and thet only adopted a means of not pairing people on the same score.

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Re: Swiss Pairing Minimum Numbers?

Post by Ian Thompson » Sat May 28, 2022 12:50 pm

Francis Fields wrote:
Thu May 26, 2022 5:12 pm
The point of the Swiss pairing system ( as believed to be devised by Arpad Elo ) is to aim to pair players of similar strength.
No. The point of the Swiss pairing system is to find the most deserving winner of a tournament. It is used when there are too many players for an all-play-all and a knockout event is not wanted.

It's reasonably good at finding the best and worst players in a tournament, provided there aren't too many players compared to the number of rounds. It's not at all good at ranking players who finish in a middling position.

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Joey Stewart
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Re: Swiss Pairing Minimum Numbers?

Post by Joey Stewart » Sun May 29, 2022 5:47 pm

Ian Thompson wrote:
Sat May 28, 2022 12:50 pm

It's reasonably good at finding the best and worst players in a tournament, provided there aren't too many players compared to the number of rounds. It's not at all good at ranking players who finish in a middling position.
That's true, I've played many tournaments where I've had a bad start and been rewarded with incredibly generous pairings for the rest of the event and meanwhile the top seeds are getting relentlessly difficult games throughout and often falter late on because of it.
Lose one queen and it is a disaster, Lose 1000 queens and it is just a statistic.

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Re: Swiss Pairing Minimum Numbers?

Post by Francis Fields » Wed Jun 01, 2022 3:16 pm

I have never been in a tournament with many unrated players and consider that thought to be insignificant. Why people should think that there needs to be a tournament format other than all-play-all does not need considering.

The winner can be governed by the format of the tournament as tie-break rules have demonstrated.

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John Upham
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Re: Swiss Pairing Minimum Numbers?

Post by John Upham » Wed Jun 01, 2022 4:12 pm

Francis Fields wrote:
Wed Jun 01, 2022 3:16 pm
Why people should think that there needs to be a tournament format other than all-play-all does not need considering.
All we need now is Stanley Unwin to translate the above.

Here it is in Cockney
Why people should 'hink 'ha' 'here needs 'o be a 'ournamen' fawma' o'her 'han all-play-all does no' need considerin.
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Francis Fields
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Re: Swiss Pairing Minimum Numbers?

Post by Francis Fields » Mon Jun 06, 2022 2:54 pm

Are you saying that Cockney is a language?

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John Upham
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Re: Swiss Pairing Minimum Numbers?

Post by John Upham » Mon Jun 06, 2022 3:37 pm

Francis Fields wrote:
Mon Jun 06, 2022 2:54 pm
Are you saying that Cockney is a language?

I'll leave that for you to decide.
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Simon Rogers
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Re: Swiss Pairing Minimum Numbers?

Post by Simon Rogers » Mon Jun 06, 2022 4:32 pm

David Sedgwick wrote:
Thu May 19, 2022 10:09 pm
John Upham wrote:
Thu May 19, 2022 7:04 pm
Francis Fields wrote:
Thu May 19, 2022 4:29 pm
The minimum number of chess players for a Swiss is 18. This is a calculation I considered some time ago.

The range of grades (or strong players) can change this - though only by a small number of players.
Is that regardless of the number of rounds?
John, I would suggest that you look at some earlier examples of Mr Fields's contributions to this Forum before seeking to enter into a serious discussion with him.

See for instance viewtopic.php?f=2&t=10160&p=229096#p229096 and the comment by Leonard Barden.
Before my time.
I've noticed Mr Fields has posted a few weird things in the Chess Questions Category today.

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