Author: Sylvain Renard
Date: 12:31:14 08/23/00
For future computer chess arbiters :-)
here are the complete rules of swiss system.
You can see that there is a problem with round 6 and rule B3 :
"
The difference of the scores of two players paired against each other should be
as small as possible and ideally zero.
"
Approved by the 1992 General Assembly.
A. Introductory Remarks and Definitions
A1. Rating
It is advisable to check all ratings supplied by players. If no reliable rating
is known for a player the arbiters should make an estimation of it as accurately
as possible before the start of the tournament. (to convert German Ingo or
British BCF use rating = 2840 -8 x INGO = 600 + 8 x BCF)
A2. Order
For pairing purposes only, the players are ranked in order of, respectively
a) score
b) rating
c) FIDE-title (IGM-WGM-IM-WIM-FM-WFM-no title)
d) alphabetically (unless it has been previously stated that this criterion has
been replaced by another one)
The order made before the first round (when all scores are obviously zero) is
used to determine the pairing numbers: the highest one gets #1 etc.
A3. Score brackets
Players with equal scores constitute a homogeneous score bracket. Players who
remain unpaired after the pairing of a score bracket will be moved down to the
next score bracket, which will therefore be heterogeneous. When pairing a
heterogeneous score bracket these players moved down are always paired first
whenever possible, giving rise to a remainder score bracket which is always
treated as a homogeneous one.
A heterogeneous score bracket of which at least half of the players have come
from a higher score bracket is also treated as though it was homogeneous.
A4. Floats
By pairing a heterogeneous score bracket, players with unequal scores will be
paired. To ensure that this will not happen to the same players again in the
next round this is written down on the pairing card. The higher ranked player
receives a downfloat ( ), the lower one an upfloat ( ).
A5. Byes
Should the total number of players be (or become) odd, one player ends up
unpaired. This player receives a bye: no opponent, no color, 1 point. A bye is
considered to be a downfloat.
A6. Subgroups
To make the pairing, each score bracket will be divided into two subgroups, to
be called S1 and S2. In a heterogeneous score bracket S1 contains all players
moved down from a higher score bracket. In a homogeneous score bracket S1
contains the higher half (rounding downwards) of the number of players in the
score bracket.
The number of players in S1 will be indicated by "p", indicating the number of
pairings to be made. In both cases S2 contains all other players of the score
bracket. In both S1 and S2 players are ordered according to A2.
A7. Color differences and color preferences
The color difference of a player is the number of games played with white minus
the number of games played with black by this player. After a round the color
preference can be determined for every player.
a) An absolute color preference occurs when a player's color difference is
greater that 1 or less than -1, or when a player played with the same color in
the two latest rounds. The preference is white when the color difference is << 0
or when the last two games were played with black, otherwise black. In this case
the (obligatory) color is already written down on the score card. (This rule is
not in effect when pairing players with a score of over 50% in the last round).
b) A strong color preference occurs when a player's color difference is unequal
to zero. The preference is white when the color difference is << 0, black
otherwise.
c) A mild color preference occurs when a player's color difference is zero, the
preference being to alternate the color with respect to the previous game. In
this case the color difference is written down as +0 or -0 depending on the
color of the previous game (white or black respectively). Before the first
round the color preference of one player (often the highest one) is determined
by lot.
A8. Definition of "x"
The number of pairings which can be made in a score bracket, either homogeneous
or heterogeneous, not fulfilling all color preferences, is represented by the
symbol x.
x can be calculated as follows:
w=number of players having a color preference white.
b=number of players having a color preference black.
q=number of players in the score bracket divided by 2, rounded upwards.
If b >> w then x = b-q, else x = w-q.
A9. Transpositions and exchanges
a. In order to make a sound pairing it is often necessary to change the order in
S2. The Rules to make such a change, called a transposition, are in D1.
b. In a homogeneous score bracket it may be necessary to exchange players from
S1 and S2. rules for exchanges are found under D2. After each exchange both S1
and S2 are to be ordered according to A2.
B. Pairing Criteria
Absolute Criteria
(These may not be violated. If necessary players will be moved down to a lower
score bracket.)
B1.
a. Two players shall not meet more than once.
b. A player who has received a point without playing, either through a bye or
due to an opponent not appearing in time, shall not receive a bye.
B2.
a. No player's color difference will become >>+2 or <<-2.
b. No player will receive the same color three times in row.
Relative Criteria
(These are in descending priority. They should be fulfilled as much as possible.
To comply with these criteria, transpositions or even exchanges may be applied,
but no player should be moved down to a lower score bracket).
B3.
The difference of the scores of two players paired against each other should be
as small as possible and ideally zero.
B4.
As many players as possible receive their color preference. (Whenever x of a
score bracket is unequal to zero this rule will have to be ignored. x is
deducted by one each time a color preference cannot be granted.)
B5.
No player shall receive an identical float in two consecutive rounds.
B6.
No player shall have an identical float as two rounds before.
Note: B2, B5 and B6 do not apply when pairing players with a score of over 50%
in the last round.
C. Pairing Procedures
Starting with the highest score bracket apply the following procedures to all
score brackets until an acceptable pairing is obtained. Afterwards the color
allocation rules (E) are used to determine which players will play with white.
C1.
- If the score bracket contains a player for whom no opponent can be
found within this score bracket without violating B1 or B2 then:
- if this player was moved down from a higher score bracket apply C12.
- if this score bracket is the lowest one apply C13. in all other cases:
move this player down to the next score bracket.
C2.
Determine x according to A8.
C3.
Determine p according to A6.
C4.
Put the highest players in S1, all other players in S2.
C5.
Order the players in S1 and S2 according to A2.
C6.
Pair the highest player of S1 against the highest one of S2, the second highest
one of S1 against the second highest one of S2, etc. If now p pairings are
obtained in compliance with B1 and B2 the pairing of this score bracket is
considered complete.
- In case of a homogeneous score bracket: remaining players are moved
down to the next score bracket. With this
score bracket restart at C1.
- In case of a heterogeneous score bracket: only players moved down were
paired so far. Start at C2 with the homogeneous remainder group.
C7.
Apply a new transposition of S2 according to D1 and restart at C6.
C8.
In case of a homogeneous (remainder) group: apply a new exchange between S1 and
S2 according to D2. Restart at C5.
C9.
Drop criterion B6 and B5 (in this order) for downfloats and restart at C4.
C10.
In case of a homogeneous remainder group: undo the pairing of the lowest moved
down player paired and try to find a different opponent for this player by
restarting at C7.
If no alternative pairing for this player exists then drop criterion B6 first
and then B5 for upfloats and restart at
C2.
C11.
As long as x is less than p: increase x by 1. When pairing a remainder group
undo all pairings of players moved down also. Restart at C3.
C12.
In case of a heterogeneous group: undo the pairing of the previous score
bracket. If in this previous score bracket a pairing can be made whereby another
player will be moved down to the current one, and this now allows p pairing to
be made then this pairing in the previous score bracket will be accepted.
C13.
In case of the lowest score bracket: the pairing of the penultimate score
bracket is undone. Try to find another pairing in the penultimate score bracket
which will allow a pairing in the lowest score bracket. If in the penultimate
score bracket p becomes zero (i.e. no pairing can be found which will allow a
correct pairing for the lowest score bracket) then the two lowest score brackets
are joined into a new lowest score bracket. Because now another score bracket is
the penultimate one C13 can be repeated until an acceptable pairing is obtained.
C14.
Decrease p by 1 (and if the original value of x was greater than zero decrease x
by 1 as well). As long as p is unequal to zero restart at C4. If p equals zero
the entire score bracket is moved down to the next one. Restart with this score
bracket at C1.
D. Transposition and Exchange Procedures
Example: S1 contains players 1, 2, 3 and 4 (in this sequence); S2 contains
players 5, 6, 7 and 8 (in this sequence).
D1.
Transpositions within S2 should start with the lowest players, with descending
priority:
a) 5-6-8-7;
b) 5-7-6-8
c) 5-7-8-6
d) 5-8-6-7
e) 5-8-7-6
f) 6-5-7-8
g) 6-5-8-7, etc.
Hint: put all numbers constructable with the digits 5, 6, 7 and 8 in ascending
order.
D2.
When applying an exchange between S1 and S2 the difference between the numbers
exchanged should be as small as possible. When differences of various options
are equal take the one concerning the lowest player of S1.
Exchange one player Exchange two players
S1 S1
4 3 2 3+4 2+4 2+3
5 a c f 5+6 j l o
6 b e h 5+7 k n q
7 d g i 6+7 m p r
The above matrices contain the sequence in which exchanges should be applied.
Exchanging one player: a) 4 and 5; b) 4 and 6; c) 3 and 5; etc. until i) 2 and
7.
Exchanging two players: j) 3+4 with 5+6; k) 3+4 with 5+7; l) 2+4 with 5+6 etc.
After each exchange both S1 and S2 should be ordered according to A2.
Remark: if the number of players in a score bracket is odd, S1 contains one
player less than S2. So with 7 players S1 contains players 1, 2 and 3, S2 4, 5,
6 and 7. The exchanges needed in that case can be found from the above ones
bydeducting all numbers in S1 and S2 by 1. The last column of the second matrix
has then become obsolete.
E. Color Allocation Rules
For each pairing apply (with descending priority):
E1.
Grant both color preferences.
E2.
Grant the stronger color preference.
E3.
Alternate the colors to the most recent round in which they played with
different colors.
E4.
Grant the color preference of the higher ranked player. In the first round all
even numbered players in S1 will receive a color different from all odd numbered
players in S1.
F. Final Remarks
F1.
After a pairing is complete sort the pairing before making them public. The
sorting criteria are (with descending priority)
- the score of the higher player of the pairing involved;
- the sum of the scores of both players of the pairing involved;
- the rank according to A2 of the higher player of the pairing involved.
F2.
Byes, and pairing not actually played, or lost by one of the players due to
arriving late or not at all, will not be taken into account with respect to
color, Such a pairing is not considered to be illegal in future rounds.
F3.
A player who after five round has a color history of BWW-B (i.e. no valid game
in round 4) will be treated as -BWWB with respect to E3. So WB-WB will count as
-WBWB and BWW-B-W as --BWWBW.
F4.
Because all players are in one homogeneous score bracket before the start of
round one and are ordered according to A2 the highest player of S1 will play
against the highest player of S2 and if the number of players is odd the lowest
ranked player will receive a bye.
F5.
Players who withdraw from the tournament will no longer be paired. Players known
in advance not to play in a particular round are not paired in that round and
score 0.
F6.
A pairing officially made public shall not be changed unless it violates the
absolute pairing criteria (B1 and B2).
F7.
If either result was written down incorrectly, or a game was played with the
wrong colors, or a player's rating has to be corrected, then this will only
affect pairing yet to be made.
Whether it will affect a pairing already made public but not yet played should
be decided by the arbiter.
Unless the rules of the tournament state otherwise:
F8.
Players who are absent during a round without notification to the arbiter will
be considered to have withdrawn themselves.
F9.
Adjourned games are considered draws for pairing purposes only.
F10.
In order to make the final standings the following criteria apply (in descending
priority):
- the highest number of points scored; should this be equal for several
participants prize money should be shared;
- where it concerns the first place: the best result in games played
against each other;
- the highest average rating of the opponents;
- the drawing of lots.
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