See Swiss pairing for the page where this page was an alias of.
A Swiss Tournament is a tournament where the McMahon score is not used. In theory all players in a Swiss tournament have the same options to win the tournament.
The Swiss system is so called because it originated in Switzerland: the first person to suggest the system appears to have been a Swiss citizen named Julius Müller (not to be confused with the German theologian of the same name), and the first chess tournament run under this system took place in Zürich in 1895.
MRFvR You got it right. The Oxford Companion to Chess brings "This popular system (...) was suggested by Dr Julius Müller of Brugg, Switzerland, and first used for a chess tournament at Zurich in 1895." I've heard, however, that a similar system was used way before in Japan for Go tournaments.
Swiss pairing based tournaments are primarily associated with chess, they are also used for a number of amateur go tournaments, notably the World Amateur Go Championship and National Go Individual. Also the sub tournament in the supergroup in a McMahon Tournament has many similarities with a swiss tournament.
- Round robin tournaments require N rounds, where N is the number of players minus 1. Many tournaments are limited to a single weekend which limits play to 6 rounds provided reasonable time limits (one hour per player with five 30 second byo-yomi periods). The field is then limited to seven players. Swiss Tournaments allow pairing 2 to the power of the number of rounds players (for 3 rounds 8 players, for 4 rounds 16players, for 5 rounds 32 players ...)
- Single elimination tournaments leave half the field with nothing to do after the first round. Each successive round half the field is eliminated leaving these players with nothing to do. Swiss pairing is one way to provide pairings for all players in all rounds.
- First Round: The Swiss pairing method does not mandate how players are paired for the first round, any of the Group Pairing methods may be used. In chess, fold pairing or slide pairing (see Group Pairing) is typically used. After the first round, players that won their game or received a bye are awarded one point and therefore have a score of 1. Players that lost, do not receive a point and so have a score of 0. Half of the players have a score of 1; half the players have a score of 0.
(in the unlikely event of a jigo or other problematic situation 1/2 point can be awarded)
- Second Round: Players with the same score are paired against each other using any of the Group Pairing methods. In chess, fold or slide pairing is typically used. Again, players that won their game are awarded one point and therefore have a score of 1. Players that lost, do not receive a point and so have a score of 0. There are four groups of players: those with a score of 2 (one quarter of the field), those with a score of 1 (half the field), and those with a score of 0 (one quarter of the field).
- All Subsequent Rounds: Players with the same score are paired against each other using any of the Group Pairing methods. The process is repeated till only one player has a perfect undefeated record provided there is a sufficient number of rounds. And there is a player who did not lose ny of his games.
First place is the tournament winner. Placings are based upon number of wins and if players have the same number of wins one or more tie breakers. In these tiebreakers the Mc Mahon score is replaced with the number of wins.
willemien: Because these tiebreakers (based on the swiss tournament score) can be useful to use as tiebreakers in McMahon Tournaments, I try to promote them by calling them Swiss score, Swiss SOS , Swiss SODOS, ect.
- In order to have the highest rated players meet each other in the final rounds of the tournament either fold pairing or slaughter pairing is often used. These pairings make the first rounds of the tournament quite boring as the players have significantly different strengths. McMahon Pairing addresses this problem.
- Unless the number of participants is a power of two, the number of participants with the same score will be odd for one or more rounds. An odd number of participants cannot be paired. And at least one player must be paired against a player with a different score. This may result in a different group of players with the same score having an odd number of unpaired players. The problem may thereby ripple across the score groups.
- In order to make the pairings as fair as possible, the pairing rules can become quite complicated (see, for example, the FIDE Swiss Rules). This problem is particular to chess due to the significant advantage of having the white pieces (first to play) combined with the lack of komi in chess. Due to these complications for chess pairings, the pairings are usually done by computer. Many programs are available to do this, in particular any program that can handle McMahon Pairing should be able to handle Swiss Pairing - since the Swiss Pairing is identical to McMahon Pairing with all players' starting McMahon Score set to the same value.
- If there are N participants in the tournament, Swiss pairing requires log base 2 of N rounds. For large tournaments, such as the 2008 North American Toyota Denso Oza Championship with 200 players, eight rounds are required. The tournament provided for only six rounds. For Swiss paired tournaments that have less than the required number of rounds, there will be more than one player with a record of all wins. In that case, the final ranking is usually based upon the following criteria:
Another way to overcome the problems of to many players for the number of rounds is to use /accelerated pairings.
RobertJasiek: "Swiss system" (as used in Go tournaments) deserves its own webpage because by far not all Swiss system tournaments use a Swiss pairing as described on this page. Here it is :-)