Pairing problems in long tournaments
The Australian draw has been used for decades in Australia and it works well for most tournaments which are short. But in longer tournaments, the aim of not playing an opponent again results in later games bypassing perhaps ten or more candidates for eventually a more uneven pairing, players differing markedly in their placings.
The solution adopted is to have one or more resets. The question is then how many resests and at what stage.
Barry argues that resets are just a mean towards an end : avoiding mismatches in pairings. The mismatch metric should not be via ratings, because a tournament gives opportunities for players to play better (or worse) than expected. The mismatch metric should be in terms of performance at that stage.
Barry has developed a version of AUPAIR which when considering pairings for round x+1 based on results up to round x, does two things: firstly flag a potentially bad pairing (set at win records differing by 2 or more) and secondly trying to select a better pairing. In the version sent to Paul this used the relatively easy way of going down the list, and the first bad pairing, just accept it without going any further. I am planning a better pairing method. In either version it is easy to impose a restriction that you will not play an opponent in two consecutive games, to avoid two top players tussling while an outsider creeps up. It would be harder to limit how many times a repeat might occur, and for the moment I suggest we try it and see if it is likely to be a problem — I suspect not.
There are several ways of trying to see how well this may work
- Looking at some past events and checking when the warning flags would be triggered. For the events logged here, you can press the arrow key to advance round by round and see when the special action would be triggered. The promising thing is that it may only affect a relatively small number of matches at the top and bottom of the field. An event may have the happy outcome of most players having little or no repeats, and the few repeats achieving more satisfactory pairings for determining top places, and the pour souls at the bottom not being faced with increasingly better opponents.
Try these for yourself: 2022 Oz 2019 Oz 2021 Vic Champ 2018 Youth which had two resets.
You can download the revised AUPAIR program AU615G and the TOU files 22OZ.tou 19OZ.tou 21VIC.tou 18YC.tou
You will also see to what extent the resets worked. If you use one or more resets, it is a matter for deliberation at which round to do the reset.
- Backtracking a past tournament, blanking results from round x onward, and running the new AUPAIR to see what pairings would be used. This is helpful to see but not a true revelation of how an event would run in practice.
- Trying a real tournament. Perhaps the Victorian Championship in June would be a good trial. And then later the Queensland Championship might use the same program or a tweaked version.