### Wsl_F's blog

By Wsl_F, history, 3 years ago, ,
UPD 2 Sep 2018

Hi guys! As I mentioned on previous contest I'm working on tool that predicts rating changes. I'm happy to present it now!

A huge amount of your nerve cells die every time when you wait for a rating update on Codeforces. Stop this! From now you could use this service, it calculates approximate rating changes for every contestant.

The most interested thing for you is extension. It partly modifies the contest standings page and shows approximate rating changes for every contestant. It is available for three browsers:

Extension in work:

Also you could find more detailed information (seed, rank, expected delta, etc.) here.

A project still in beta, so predictions are not very accurate. Average mistake around 5 points, but for the contestants at the back of standings it could be greater up to a few hundreds.

Tech details

I'd like to thank Rubanenko and all other members of NBHEXT developers team for your shared sources and MikeMirzayanov for the great Codeforces platforms with shared API & ratings formulas.

AWESOME UPD

Prediction for todays contest (cf #399) is absolutely matching real rating changes! Thanks for AlexDmitriev! He was close to find my bug in rating calculation:)

UPD

Thanking KieranHorgan now CF-Predictor has a new design. Check it out:)

• +187

 » 3 years ago, # |   0 Maybe I miss something but why use this, when there is NBHEXT? Did you overcome some of its bugs? Please, give more information on how this differs from NBHEXT :)
•  » » 3 years ago, # ^ |   +27 NBHEXT not working
•  » » » 3 years ago, # ^ |   0 My bad, I didn't know :)
•  » » 3 years ago, # ^ |   +23 NBHEXT predicts rating changes using your browser (did you notice that your browser works slowly and is lagging while doing predictions?) CF-Predictor extension get prediction from own server, so all calculation are made on serverside. And yes, NBHEXT is not working now :(
•  » » » 3 years ago, # ^ |   +5 Now I see, thanks :)
 » 3 years ago, # |   0 Not for Mozilla? Please make it for Mozilla too.
•  » » 3 years ago, # ^ |   0 It is on validation now. I hope, it doesn't take lot of time:)
 » 3 years ago, # | ← Rev. 3 →   -7 deleted.
•  » » 3 years ago, # ^ |   +11 You know, browser extensions work that way that you can enable and disable them whenever you want.
•  » » » 3 years ago, # ^ |   0 Yeah, my bad.
 » 3 years ago, # |   +13 Funny, on attached screen all but one prediciton were good with tolerance of two points, but tourist's prediciton was way off (by 46 points). Probably there is a bug that comes to light only when we are dealing with very high rated users. Maybe you did same bug as original bug thanks to which tourist once exceeded 4000 points :)?
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 Maybe I did not understand bug correctly, but wasn't the rating change caused by tourist beating himself? If it's the same bug, wouldn't the prediction show him as losing more rating, because he lost to himself instead?
•  » » » 3 years ago, # ^ |   0 Nope. You only get the probability of him beating himself, no matter what places the others take. http://codeforces.com/blog/entry/44214
 » 3 years ago, # |   0 Please make it for Mozilla too.****
•  » » 3 years ago, # ^ |   +8 I'm afraid it doesn't happen soon.
 » 3 years ago, # | ← Rev. 3 →   +9 It seems the variance of the tool is quite high. Last contest I got an expected change of +22 (which seemed way off) and the real change was -63. I also saw people with similar results and similar starting rating getting a negative expected rating change.
•  » » 3 years ago, # ^ |   +8 This was prediction before system tests. It caused because server gets to many request and have no time to calculate new rating prediction. I will fix this prior next round. If you a curious about prediction after system tests you could see it at static page here.It predicts to you -65, 2 point lower than actual results.sorry for my bugs
•  » » » 3 years ago, # ^ | ← Rev. 2 →   +5 What about showing the last update time of the prediction so that people can know more about it, and also how the prediction should be considered as accurate. For instance, from the last update time shown, people can know if the prediction is about middle of the contest, end of contest but before systest, or after systest. So it is much more clear.I hope you can consider adding something like this. Thanks for such a great tool anyway:)
 » 3 years ago, # |   0 Auto comment: topic has been updated by Wsl_F (previous revision, new revision, compare).
 » 3 years ago, # |   +1 Apparently, the rating site is down (at least for me). Any ideas why?
 » 3 years ago, # |   +1 The site is up now. But when I try to select a contest and click "Get rating prediction", the results won't display at all. The browser seems to load infinitely instead.
•  » » 3 years ago, # ^ |   0 Site is again down now. :|
 » 3 years ago, # |   0 I think I found a bug. See this — He is in my starred user list, He submitted A and got WA on pretest 1 [skipped]. But will this even happen? He will get near +77? o.O
•  » » 3 years ago, # ^ |   0 Yeah, you are right this is bug. mdshs.shanto has a quite low rating (887) and my program calculated his seed as 2922. He took place much higher, so his rating should increase. But official cf rating works somehow different, and I don't know where my mistake((
•  » » » 3 years ago, # ^ | ← Rev. 2 →   0 Maybe in case of several people on the same place from A to B, you consider their rank to be A, while it's probably considered as (A + B)/ 2;
•  » » » » 3 years ago, # ^ |   0 I will check this, but in the official shared code rank calculates as in standings:  private void reassignRanks(List contestants) { sortByPointsDesc(contestants); for (Contestant contestant : contestants) { contestant.rank = 0; contestant.delta = 0; } int first = 0; double points = contestants.get(0).points; for (int i = 1; i < contestants.size(); i++) { if (contestants.get(i).points < points) { for (int j = first; j < i; j++) { contestants.get(j).rank = i; } first = i; points = contestants.get(i).points; } } { double rank = contestants.size(); for (int j = first; j < contestants.size(); j++) { contestants.get(j).rank = rank; } } } 
•  » » » » » 3 years ago, # ^ | ← Rev. 2 →   +5 If all people get same number of points, this code will return contestants.size() as far as I understand the code. In standings everybody would be first
 » 3 years ago, # | ← Rev. 2 →   0 Excellent Work! Forked it as Well :)
 » 3 years ago, # |   +11 Your tool was perfectly worked yesterday! Thanks man!
 » 3 years ago, # |   +13 I suggest to add a Disable/Enable button for the extension as sometimes i wanna to hide it during the contest
 » 3 years ago, # |   +3 Site is down.I am unable to open it
 » 3 years ago, # |   +13 Shows 0 to me ?
•  » » 3 years ago, # ^ | ← Rev. 2 →   0 Yept, maybe because of some problems on the server. Lets hope it will be fixed as soon as possible :)
•  » » » 3 years ago, # ^ |   0 *ept
 » 3 years ago, # |   0 Now a days, it's not working sometimes. Please pay attention to this. Thanks :-)
 » 3 years ago, # |   +10 It's still not working!!!
 » 3 years ago, # |   0 CF-Predictor seems to be working now but rating change for #431 Div.2 is wrong. Why?
•  » » 3 years ago, # ^ |   0 The predictor has you placing 289 when your official placing is 338.The placing of several top participants appear to be out of order on the predictor.
 » 3 years ago, # |   0 Can sombody help me set this extension up...I added it to chrome extentions...but dont know how it works
•  » » 3 years ago, # ^ |   0 You should just open standings page of active or recently ended contest. You will see a rating change in the last column. For example: last contest here PS Probably you have a slow internet connection, in this case downloading data could take a while.
•  » » » 3 years ago, # ^ |   0 Thats an amazing extension...Almost accurate it showed +20 and I got +21...You did an amazing job
 » 3 years ago, # | ← Rev. 3 →   +18 I think the web interface is really ugly now... UPD: Great interface now.
•  » » 3 years ago, # ^ |   +8 I'm sorry, I'm 100% noob in the frontend. Do you have any better proposal for start page design?
•  » » » 3 years ago, # ^ |   +2 Just use plain text, no fonts, no styles.
 » 3 years ago, # |   +3 Auto comment: topic has been updated by Wsl_F (previous revision, new revision, compare).
 » 2 years ago, # |   +5 Please predict the Good Bye 2017 round's ratings, taking into account the changed ratings due to the last Educational round.
 » 2 years ago, # |   +71 Please update it to the new rating system.
•  » » 2 years ago, # ^ | ← Rev. 2 →   +28 I think they have updated it for Div.2 and Div.3 according to the new rating system, but forgot educational rounds :(
•  » » » 2 years ago, # ^ |   0 Isn't it the first educational round since new rating was introduced?
•  » » » 2 years ago, # ^ |   +11 Hi! Could you please tell more specific, what doesn't work?
•  » » » » 2 years ago, # ^ |   +11 In educational rounds rating changes for purple users aren't shown.
•  » » » » » 2 years ago, # ^ | ← Rev. 2 →   +24 Thanks! I didn't notice this change:) UPD: Fixed
•  » » » » » » 2 years ago, # ^ |   +15 Sorry for the late answer, thanks to you too :)
 » 2 years ago, # |   +13 Wsl_F, it seems that the extension doesn't work for HTTPS version of Codeforces. Please fix.
•  » » 2 years ago, # ^ | ← Rev. 2 →   +22 Thank you! Updated for Chrome & FireFox! There is some issues with opera. I don't know how soon it be solved.
•  » » » 2 years ago, # ^ |   +6 Thanks for the fast update, it works now. Tested on Firefox 60.
•  » » » 2 years ago, # ^ |   +8 Wsl_F, It's still not working on my chrome for HTTPS version :(
•  » » » » 2 years ago, # ^ |   +8 skmonir, could you please check version of extension? It should be 1.2.3
•  » » » » » 2 years ago, # ^ |   +8 Wsl_F, yes. It's 1.2.3. In fact, when it wasn't working, I removed it and added again from the chrome web store. So it's latest version.
•  » » 2 years ago, # ^ | ← Rev. 2 →   +9 You are right. But we can visited this url to find our rating changes.
 » 23 months ago, # |   +4 It can't work now.
•  » » 23 months ago, # ^ |   +10 Do not worry, everything is fine :) I'll turn it on before the next contest. Free heroku account gives you a limited amount of free hours per month, so I need to spend them wisely :)
•  » » » 17 months ago, # ^ |   0 Have you considered Azure Web Services? Don't know if it would work for you, they offer a 1 year free license for students, with a variety of services
 » 23 months ago, # |   +1 What about Microsoft Edge user???
•  » » 21 month(s) ago, # ^ |   0 Hello!I'm a Microsoft Edge user, too. I use tampermonkey to install CF-Predictor on my computer.You can install tampermonkey here -> https://tampermonkey.net/And then install CF-Predictor here -> https://greasyfork.org/zh-CN/scripts/38050-cf-predictorI hope it will help you.
 » 21 month(s) ago, # |   +3 Auto comment: topic has been updated by Wsl_F (previous revision, new revision, compare).
 » 19 months ago, # |   -9 Why not for safari...???
 » 17 months ago, # |   +1 In case the post is too long and it's hard to find links, this is a summary: It calculates approximate rating changes. Extension: Chrome, Opera, Firefox. For Microsoft Edge use Tampermonkey. Elasticbeanstalk site (only run in the contest's days) Source code. Thanks to NBHEXT (source code) New design (online front-end).
 » 17 months ago, # |   0 The predictor was working fine till yesterday. However, today I updated my Firefox web browser and it's not working anymore. I am running Firefox Quantum (64.0) in Ubuntu 18.04.
•  » » 17 months ago, # ^ |   +8 no, that's just because the server for cf predictor crashed
•  » » » 17 months ago, # ^ |   +8 Phew... I thought the newer version is not supported and so I have to reinstall the outdated one.
 » 17 months ago, # |   +7 Got Safari and want to stick with it....
 » 16 months ago, # | ← Rev. 2 →   0 Wsl_F there seems to be some error in rating predictions specially in the latest educational round. Please have a look into this!
 » 16 months ago, # |   +3 Extensions, get you out of "tension".
 » 16 months ago, # | ← Rev. 3 →   +1 Wsl_F has the CF rating system is being changed.In last contest predictor showed -7 rating change.But it was actually -23
•  » » 16 months ago, # ^ |   +1 Something similar happened to me too.
 » 15 months ago, # |   +4 Wsl_F CF-Predictor hasn't been working for me lately(it doesn't display the delta column)I'm using Google Chrome and I tried uninstalling and installing it back, but still no success.
•  » » 15 months ago, # ^ |   0 I have the same problem with chrome. I have downloaded the Mozila Firefox, where the predictor works.
•  » » » 15 months ago, # ^ |   0 Same here with Google Chrome is not working.Version 73.0.3683.75 (Official Build) (64-bit) for more info
•  » » 15 months ago, # ^ |   0 yeah, me too!
•  » » 15 months ago, # ^ |   0 I guess we'll have to go back to the tried-and-true method of "Look at your rank and guess the expected delta and then pray you get high rating"
•  » » » 15 months ago, # ^ |   +8 I like your approach! suffering is madatory party of competitive programming :D But if you like, website with predictions still works.
•  » » 15 months ago, # ^ | ← Rev. 2 →   +8 Thank you for reporting, I'll look on this.UPD I've found the reason of issue. In last chrome update they changed Cross-Origin Read Blocking policy. And the actual problem is that I can't update code ASAP. I recently started working in Google and they have pretty strict policy about open source projects. I'll try to come up with some solution, but sorry, no promises.Current solution is to use website.
•  » » » 14 months ago, # ^ | ← Rev. 3 →   +12 Hi Wsl_F, I have fixed the CF-Predictor Chrome extensions and it is working on Chrome 73. I am sending you a PR, please review it and if possible update the Extension as soon as possible.UDP1YOU SHOULD REALLY WAIT FOR OFFICIAL RELEASEFor those who want to test it now, Download this, Uninstall the old version as they are signed with different keys. Follow this tutorial on how to manually install chrome extensions. (It's easy).UDP2To install official extension again, you must remove thisUDP3The new extension is available in the chrome store. Update now
•  » » » » 14 months ago, # ^ |   0 Thank you a lot! Extension has been updated (version 1.2.4) and now it works fine!
 » 14 months ago, # |   0 Thanks，it'useful.
 » 12 months ago, # |   0 The add-on used to work on Firefox Android but now I can't even download it!
•  » » 2 months ago, # ^ |   0 Update your Firefox. It worked for me.
•  » » » 2 months ago, # ^ |   0 Thanks. I looked it up and found the solution months ago.
 » 10 months ago, # |   0 Excuse me,can anyone tell me the exact rating calculation formula?
 » 9 months ago, # | ← Rev. 2 →   0 Why is the old rating of the user Legilimens2019 at https://cf-predictor-frontend.herokuapp.com/roundResults.jsp?contestName=Codeforces+Round+%23580+%28Div.+1%29&contestId=1205&sbm=Get+rating+prediction 1500 while the correct value is 2303?User Hamsterw also has incorrect value of old rating.
 » 9 months ago, # |   0 I have a suggestion to improve CF predictor. First of all thank you for the amazing extenion. Feature: Add rating change for virtual contest. you could color the rating with red or any color to show that it is virtual
 » 7 months ago, # |   +34 In the recent contest Codeforces Global Round 5, the rating prediction is wrong for a user with negative rating. (predicted -48, real -4)Possible reason: the binary search algorithm (getRatingToRank function) in the official code initialize the left variable to 1, so the result is incorrect for values < 1.
•  » » 4 months ago, # ^ |   +15 Mike pls fix
 » 5 months ago, # |   0 Its not working on Opera mini web browser
 » 4 months ago, # |   0 I'm having some problems in the extension, its not working in Opera but works in Chrome. Can someone help me more with opera?
•  » » 4 months ago, # ^ |   +8 It was not working for me too. I installed an extension that helps to download Chrome's extensions, here is the link https://addons.opera.com/en/extensions/details/install-chrome-extensions/then you can download Chrome's predictor and it will work perfectly.
•  » » » 4 months ago, # ^ |   +3 thanks, I tried to open chrome web store,from Opera browser, and from the extentions I downloaded the CF-predictor and it worked.
 » 4 months ago, # |   +57 I think that something is broken :(
•  » » 4 months ago, # ^ |   +8 Yes, for some users, it takes 1500 rating as previous rating. Seen here: https://cf-predictor-frontend.herokuapp.com/roundResults.jsp?contestName=Codeforces+Round+%23618+%28Div.+1%29&contestId=1299&sbm=Get+rating+prediction
•  » » » 4 months ago, # ^ |   +21 Yeah, it happened because of New Year magic with the possibility to rename accounts. It should be fixed by now.
 » 4 months ago, # |   0 It doesnt work in virtual participant. Can you help me ?
•  » » 4 months ago, # ^ |   0 Sorry, but it doesn't suppose to work for virtual contests because it would generate additional load on the server.
•  » » » 4 months ago, # ^ |   0 Ok
 » 4 months ago, # |   0 thanks for CF-Predictor
 » 4 months ago, # |   +23 How is it possible that this post isn't +1000?
 » 4 months ago, # |   +3 I've edited the JS File a bit so that it works in Safari ( macOS Catalina ). See the full details here
 » 4 months ago, # |   0 Sorry but can it predict at the moment we chose ?
 » 3 months ago, # |   +10 What happen to me ;-; It doesnt show anymore ;-;
•  » » 3 months ago, # ^ |   +6 i suppose all profiles are temporary blocked and cfpr needs ratings to work?
•  » » » 3 months ago, # ^ |   +8 Oh, maybe it is. I use this a lot and get confused when it doesnt work haha ~~
•  » » » 3 months ago, # ^ | ← Rev. 2 →   0 Your rating change is a function of the ratings of the participants in the contest you did. It follows that the predictor needs ratings to operate, which, among other cf features were not present during the contest.
 » 2 months ago, # |   0 Firefox extension not working? Shows add-on appears to be corrupt. How to fix this?
 » 2 months ago, # |   +5 It showed -48 for me and -62 for my friend but we both got -16
 » 2 months ago, # |   +34 Hey, the rating predictor isn't predicting correct delta. Can you please fix it. Thanks.