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Author Topic: ELO Rating  (Read 4069 times)

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December 14, 2009, 11:20:11 AM
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TheJord

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ELO Rating
« on: December 14, 2009, 11:20:11 AM »
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
"The rule of Gondor is mine!"

December 14, 2009, 01:14:40 PM
Reply #1

TheJord

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Re: ELO Rating
« Reply #1 on: December 14, 2009, 01:14:40 PM »
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
"The rule of Gondor is mine!"

December 14, 2009, 03:28:40 PM
Reply #2

Sete

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Re: ELO Rating
« Reply #2 on: December 14, 2009, 03:28:40 PM »
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! :D

Cheers Jord!

December 14, 2009, 08:41:01 PM
Reply #3

chompers

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Re: ELO Rating
« Reply #3 on: December 14, 2009, 08:41:01 PM »
Ah maths - you've got ot love it :)

December 14, 2009, 09:16:15 PM
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Sete

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Re: ELO Rating
« Reply #4 on: December 14, 2009, 09:16:15 PM »
Ahahah, or hate it... ;P

December 15, 2009, 12:03:39 PM
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Jerba

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Re: ELO Rating
« Reply #5 on: December 15, 2009, 12:03:39 PM »