The Ladder is a list of positions, with each position occupied by one player.
The ladder analogy comes from showing the player pairings as a collection of rungs, with two players per rung. Position 1 is left-most player at the top of the Ladder. If there are an odd number of players (an Odd Ladder), the player in position 1 is placed alone on the first rung of the Ladder and the second rung is occupied by the players in positions 2 (left-side) and 3 (right-side).
Each new round is generated as a result of match play in the previous round, plus changes due to players adding and dropping. There are two ways in which pairings for the next round can be generated. The Rio Rancho 14.1 Ladder ladder now uses the Win / Rand method to generate the next round. (It morphed from the Traditional method to the Win / Rand method in order to reduce repeat match-ups between players.)
Here are descriptions of the two ways of generating the positions for the next round.
With the Traditional method the winner of a match moves up a rung to the right, while the loser moves down and to the left (often referred to as Up-right, Down-left). Of course the top and bottom rungs of the ladder are exceptions. The top rung match sees the winner stay left-most (first-position), while the bottom rung sees the loser stay right-most (last position).
A text diagram of (numbered) positions on two sample ladders (one "Even", and one "Odd") follows. Note that the number associated with a position maps to the player's rank on the ladder.
---- Diagram of Even and Odd ladders ----
Numbers show ladder player rank for the round.
(PID 0 is an ID number for internal use only.)
Even Odd
-----------------------------------------
left right RNG left right
--------------- ---------------
1 2 1 1 0 *
3 4 2 2 3
5 6 3 4 5
7 8 4 6 7
-----------------------------------------
* 0 is a place holder for the winner
winner of the second-rung match.
DROPs then ADDs are done after the positions have been shuffled according to win-loss results of scheduled matches.
The Win / Rand method was developed to reduce frequent repeat-pairings of players. If a repeat pairing is made it goes for the oldest one it can find.
Unlike the Up-right, Down-left movement used in the Traditional method, DROPs then ADDs are done before generating new pairings.
A "Winner" pool and a "Random" pool are created based on the results of the previous round. People ADDing to the ladder go into the "Random" pool.
Players from the "Winner" pool populate the left side of each rung (exceptions being the first or second rung as shown below). They will be paired with players from the "Random" pool in a way that reduces repeat-pairings. (When the pools are not of equal size some skewing will happen.)
A text diagram of (numbered) positions on two sample ladders (one "Even", and one "Odd") follows. Note that the number associated with a position maps to the player's rank on the ladder. (The pairing method used here doesn't reflect a player's performance as it would in the Traditional method. Reviewing the various statistics collected for each player would be a better way to track performance.)
---- Diagram of Even and Odd ladders ----
Numbers show ladder player rank for round.
-----------------------------------------
Even Odd
left right RNG left right
--------------- ---------------
1 2 1 1 0
3 rand 2 2 3
4 rand 3 4 rand
5 rand 4 5 rand
... ... ... ... ...
rand rand last rand rand
-----------------------------------------
The last line (or 'rand' entreis is a
likely result -- it depends on number
of previous round winners and losers
after Drops & Adds.