Silver_Fox's blog

By Silver_Fox, history, 12 days ago,

Hello, Codeforces!

I'm new on AtCoder and was interested, what rating would I normally get there after participating in CodeForces rounds, and how does rating on these two sites correlate.

Of course, there is a correlation ;)

Link to some plots and dependencies:

Rating correlation plots

preview:

And now you can get a prediction for the site you are new to.

Here is CodeForces <-> AtCoder rating converter:

Rating converter

preview:

You can send any suggestions to this e-mail:

[email protected]

• +269

 » 12 days ago, # |   +6 Thanks to misha_sh for help with this!
 » 12 days ago, # |   +15 I took AtCoder accounts which have link to corresponding CodeForces handles. Then selected only those who have at least 7 writed contests on both. It may take much longer than 7 contests for AtCoder rating to converge. My AtCoder account https://atcoder.jp/users/ssvb/history currently participated in 10 ranked contests and has provisional rating 654. Average of the numbers from the "performance" column is 795 (~22% higher than the provisional rating). And I have no idea how many additional contests are necessary for my AtCoder rating to stop being considered provisional.
•  » » 11 days ago, # ^ |   0 Yes, thanks, it really changes the result a bit. Something like +60 to result when converting CF to AC rating, so the difference is not so big (updated in converter)
•  » » » 11 days ago, # ^ |   +8 According to this it will take at least 10 rounds for it to converge, for me personally it took 12 rounds for the warning of "rating not converged yet" to disappear.
•  » » 11 days ago, # ^ |   +52 Several aspects of the AtCoder rating system are briefly described in "rating.pdf" in the dropbox linked as "AtCoder's Rating System" on their front page. The most important thing to note is that the displayed user ratings are less than the internal weighted-performance-average used for calculation purposes, according to the following formulas: $\text{displayed rating} = \text{performance average} - f(\text{number of rated contests})$ $f(n) = \frac{F(n) - F(\infty)}{F(1) - F(\infty)} \times 1200$ $F(n) = \frac{\sqrt{\sum_{i=1}^n 0.81^n}}{\sum_{i=1}^n 0.9^n}$Note that $f(10) \approx 157$ and even $f(30) \approx 15$, so this really ought to be accounted for explicitly unless you limit consideration to only accounts with quite a lot of rated rounds. Codeforces started using a similar system last year, but it has $f(n) = 0$ for all $n \geq 6$, so no such correction should be necessary.AtCoder also applies some monotonic transformation to ensure that all displayed ratings are positive, but I don't have any knowledge of what transformation that is, exactly.
 » 12 days ago, # |   +14 Thanks great project ! Tho I am interested to know the formula / maths behind the conversion.
•  » » 11 days ago, # ^ |   0 I think the author used something like "Linear Regression" to find out the correlation.
•  » » » 11 days ago, # ^ |   0 Something like that, since it's the easiest and the most working solution.
 » 11 days ago, # |   -8
 » 11 days ago, # |   +15 This mapped my max CF and AC rating pretty closely. Nicee
 » 11 days ago, # |   +8 There is an interesting blob at 2100 Codeforces — 2000 AtCoder.I hope I will get there someday.
 » 11 days ago, # |   +18 I instantly recognize jh05013.
 » 11 days ago, # |   +5 Got such a big difference:ATC -> CF: 1537 -> 1928 (lol)CF -> ATC: 1603 -> 1108
 » 11 days ago, # |   0 Pretty correct ig. But tbh it is easier to get rating from ABC/ARC and sole div.2 from the sites, making it harder to determine.