ELO Rating

[TheJord]

For those interested in the maths behind your rating

For information, the ELO formula is as follows:

Say the rating of the better player is r1 and the rating of his opponent is r2. The probability that the higher ranked player wins (let us call this number P_F) can be computed by

P_F = 1 - 1/(10^(D*SQRT(n)/2000)+1)

where

n = the length of the match
D = absolute value of the current rating difference between both players = ABS(r1-r2)

The new rating of both players become then as follows:

a) If the higher ranked wins the match:

r1 + 4*SQRT(n)*(1-P_F) for the winner

r2 - 4*SQRT(n)*(1-P_F) for the loser

b) If the underdog wins the match:

r1 - 4*SQRT(n)*P_F for the loser

r2 + 4*SQRT(n)*P_F for the winner

All players start at rank 1500

[TheJord]

We actually use a much simpler version

» Using the old ratings oldA and oldB, the win probability for team A is calculated:
prob = 1.0 / (1 + 10 ^ ((oldB-oldA)/400.0))
» he change in the ratings is then calculated by:
score = 1 if A wins, 0.5 for draw, 0 if B wins
diff = 50*(score-prob)
» After that some rounding magic to integer is applied and the new ratings are calculated:
newA = oldA+diff, newB = oldB-diff

[Sete]

Okay, I got lost somewhere in the middle... :/

Anyway, could you point me to the site you use? I'd like to run some "home made" leagues and it would be just great!

Cheers Jord!

[chompers]

Ah maths - you've got ot love it

[Sete]

Ahahah, or hate it... ;P

[Jerba]

Ah maths - you've got ot love it

Makes me think of this: http://www.youtube.com/watch?v=Pj2NOTanzWI

lol