How many rounds in a tournament?

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21

Sorry, I don’t mean to put you on the defensive. I mainly just tagged you since I thought you might be interested to see this counter-example.

I just want to understand how long a Swiss tournament might last. I think @Groin summed it up well above:

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22

I don’t think this is quite right as that would be a round robin which would only be for the smallest tournament IRL.

In think this is it. IRL you have some fixed number of rounds and the TD will arrange the pairings so that a winner is not determined too soon but ensuring that the final round is decisive. However on OGS the pairings are done automatically and there are more disqualifications (losses on time for example) than IRL so I guess it can’t work like that.
(MacMahon tournaments and pairings are also odd on OGS)

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23

Ok I reviewed my classics https://senseis.xmp.net/?SwissPairing

Quite detailed.
(copy/paste:)
Using this rules gives the following table

Rounds players number of places validated
6 26 1
6 19 2
6 12 3
7 17 3
8 24 3
9 31 3
An other approximation is:

The number of rounds for a Knock out plus 2 rounds per validated place

24

From looking through a few pages of history, it seems like 6-person Swiss tournaments always last four rounds, even if people drop out.

Here’s an example that had only 3 participants left after round two, and just 2 for the final round:

For more tournament pedant trivia, it’s interesting that Hacker_Denay played no moves, was “disqualified” in round two, had the fourth-highest score, and still won the third-place trophy.

Here’s a 4-person tournament that had three rounds:

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25

I looked around some more and the tournaments I can find seem to be consistent with the formula floor((P+2*7)/5) limited to a maximum of 8 rounds.

This formula predicts that P=21 would be the first tournament with 7 rounds, and P=26 would be where they reach the max of 8 rounds.

EDIT: found one with P=21, and it worked! (From a three-year-old question here.)

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26

Looks like the max is NOT 8 after all since this one fits floor((P+2*7)/5):

(In my previous example with P=36 it must have stopped early because all but one of the players were disqualified.)

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