Life In 19x19

The Jena tournament, an EGF Grand Prix event, has a new tournament system.

JIGS System:
McMahon tournament in which the first 16 players (in first round, and 8 players in second round, …) are force-paired as in a knockout tournament. (Players who lose a game in the knockout part will continue to play in the McMahon tournament with all other players.)

The best four players are seeded according to rating, the remaining 12 players will be grouped by lottery just before the first round starts.

The first four places are decided after 4 rounds. All other places are decided by McMahon ScoreX.

Komi for all games is 6.5 Points

What do you think about this system? Maybe you didn't understand how it works yet.

You have 4 pools, each with 4 players. Each pool contains one of the top 4 seeds.
The first 2 rounds of the tournament will decide the winner of each pool. At the end of round 2 we have 4 players in the lead, after round 3 that becomes 2 players, and after round 4 just 1 player. At this point, even though there is 1 round left, places 1 through to 4 are decided.
Round 5 decides things for the other players.

I wonder what the motivation to have a knockout tournament inside a McMahon event is. Moreover, why not just have a classic Split or Fold seeded knockout tournament? The system doesn't seem obviously better than a normal McMahon to me. Given that 5 Grand Prix points places, not 4, are available to the participants, it seems a touch over-engineered to me.

We used roughly the same system in Groningen for a number of years starting about 15 years ago, with 16 players playing knock-out, 12 dropping back to the main McMahon tournament if they lost in the first 2 rounds on Saturday while the remaining 4 players took the main prizes. We did a classic split and fold though.

Main advantages were that there is never a tie for the main prize (500 euro then) and that the top group could play with extra time (90 minutes + 30s byoyomi) doing only 4 rounds, while the McMahon played 5 rounds with 60m + 20s byoyomi.

All in all I think it worked reasonably well, and we got a lot of positive feedback from the top contenders (especially about the extra time allotment)

I don't understand the reasoning behind the initial lottery, but clearly a knockout is indeed very nice if you want a clear winner. Mainly it's this tournaments inclusion in the Grand Prix that makes me feel that this system is a bit odd. 4 places decided by knockout, 1 place by McMahon. I suppose it tends more to being unusual rather than being bad.

The main problem in deciding the N first players of a tournament are players who miss rounds.
With this system, it seems to me that the players are strongly encouraged not to miss any round. That's a good thing.

I wonder what they do if one of the top players decides to miss a round all the same. Forfeit win for the opponent, I guess. With the usual McMahon system, we can find another opponent.

I don't think that is a problem, not if you are going to apply the rule "You can only start above the McMahon bar (or in the top group) if you play in all rounds of the tournament." I thought that it was a common rule.

Maybe... but I wasn't aware of it until a month ago.
Would you have some resources about tournament systems ? The most complete that I found is the one by the British Go Association (http://www.britgo.org/organisers/handbook/tournament), but this rule is not mentioned at all.

Senseis Library has some pages which are okay. Surprisingly neither the BGA handbook, nor https://senseis.xmp.net/?McMahonPairing%2FBarTheory, mention the must play all rounds criteria. Perhaps the manuals of the pairing programs mention this.

Wow, thanks a lot. That's a lot of useful info.

It is mentioned in the BGA handbook

4.4 Sleeping Players
A player who misses a round (with the tournament director's consent) sleeps for that round. For the purpose of producing the pairing, a sleeping player is deemed to have achieved an average score for each round missed. In order to prevent biassing the draw by pairing players who sleep, an extra McMahon point is awarded after every two rounds missed. This score increase does not count as a win.

In more important tournaments, players in the top McMahon group (or Supergroup if there is one) are not allowed to sleep for any round. Sleeping players who would be in the top group are removed by reducing their initial McMahon score by one or possibly two points. This prevents the lower group players from interfering with top group players in later rounds.

I never really understood why the software could not cope with adding half a point for each round missed

Oh, I missed that.

For tournaments, I use the Open Gotha software. It allows to add half a McMahon point, or a full McMahon point, or a win or half a win, or nothing, to sleeping players and/or bye players.
Since recent versions, it also allows to give zero points to sleeping players while giving half a point to the SOS of their opponent.