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EloChart

Printing the chart

I can display the chart with all players (Player Name, Elo) sorted by decreasing Elo rank.

Adding a new player

I can add a new player (Player Name). When I display the chart, the new player is displayed, with Elo rank = 1500. The Player Name must not exist already in the chart.

Recording a match

I can record a match between two players. When I display the chart, the Elo rank of each player has been recalculated. I cannot record a match between a player and herself. I cannot record a match between players that are not in the chart.

Rules for calculating Elo rank of a player

En+1 = En + Kn x (W - p(D))

D = En - F
F = Elo rank of opponent
p(D) = 1 / (1 + 10^(-D/400) )

K = 40 if n ≤ 30
K = 20 if En < 2400
K = 10 if EN ≥ 2400

W = 1 if player won
W = 0.5 if equality
W = 0 if player lost