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Here is what you get when you ask FIBS for it's rating formula:
> help formula
NAME
formula - The formulas used to calculate rating changes
DESCRIPTION
These are the formulas used to determine the ratings of a player:
Let's say that two players P1 and P2 were playing a n-point match.
The ratings of the players are r1 for P1 and r2 for P2 .
Let D = abs(r1-r2) (rating difference)
Let P_upset = 1/(10^(D*sqrt(n)/2000)+1) (probability that underdog wins)
Let P=1-P_upset if the underdog wins and P=P_upset if the favorite wins.
For the winner:
Let K = max ( 1 , -experience/100+5 )
The rating change is: 4*K*sqrt(n)*P
For the loser:
Let K = max ( 1 , -experience/100+5 )
The rating change is: -4*K*sqrt(n)*P
The 'experience' of a player is the sum of the lengths of all matches
a player has finished. Every player starts with a rating of 1500 and
an experience of 0.
SEE ALSO
ratings
>
Let's walk through this in English.
D is the difference in the two ratings. If you're rated 1850 and I'm
rated 1750, then D=100. Easy enough.
n is the match length. The real workhorse of the formula is in the
P_upset line; that calculates the probability of the lower-ranked
player winning the match.
P then becomes P_upset if the lower-rated player wins, or 1 - P_upset
if the higher-rated player wins.
K is the factor that scales for people with lower experience. Once
a player hits 400 experience, K is always 1.
So essentially, the winner get 4 * the square root of the match
length * the probability of his winning, and the loser loses that
much.
-Patti
--
Patti Beadles, Oakland, CA |
pattib@gammon.com | Going to war over religion is
http://www.gammon.com/ | basically arguing over who has the
Check out www.tribe.net! | better imaginary friend.
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