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Writer's pictureTianshan Su

Blog Entry 20 - Matchmaking & Ranking in Multiplayer Game

Updated: Mar 2, 2023

Now I'm trying to find a matchmaking system that suits our fun party game. The basic feature I want would be a fair system with few limitations.

As a result, I started my research.


1. ELO

https://www.youtube.com/watch?v=AsYfbmp0To0



  • the centre of the curve could be seen as average, the centre line is the average


  • the logistic curve

  • the more this curve is to the right of 0, the more likely that the player wins

  • ELO system: if one player is 400 more points than another player, they are 10 times more likely to win


The Winning Probability Equation:

Because B wins = (1-P(A wins)), so

Write this equation in another way, so

  • If the result is 1, then you must win; if the result is 0, then you must lose

  • When a player performs better than expected, his points will increase; the more incredible the victory (small P value), the more points he will get; the more incredible the loss (high P value), the more points he will lose


The Elo Points After the Game Equation:

When Player A = 1656; Player B = 1763

Pb’s Elo=Pb’s previous Elo +key factor(1-Pb’s winning probability)

  • Therefore, there is no advantage in scoring between strong players and weak players

  • After a long time, the ELO value of this player is very close to his real level


Pros:

  • widely used & well understood

Cons:

  • only works for 1v1 or team vs team but only based on the whole team’s point, not the individual's point

  • new players will take a long time to converge to their skill rating (long time)




2. ELO- MMR

Aram Ebtekar and Paul Liu. 2021. Elo-MMR: A Rating System for Massive Multiplayer Competitions. In Proceedings of the Web Conference 2021 (WWW '21). Association for Computing Machinery, New York, NY, USA, 1772–1784. https://doi.org/10.1145/3442381.3450091


’“MMR” stands for “Massive”, “Monotonic”, and “Robust”

  • “Massive”

    • it supports any number of players with a runtime that scales linearly

  • “monotonic”

    • a synonym for incentive-compatible, ensuring that a rating-maximizing player always wants to perform well

  • “robust”

    • rating changes are bounded, with the bound being smaller for more consistent players than for volatile players

Classically, rating systems were designed for two-player games. The famous Elo system, as well as its Bayesian successors Glicko and Glicko-2, have been widely applied to games such as Chess and Go


Pros:

  • Massively Multiplayer: the algorithm is fast and numerically stable, even with thousands or millions of individually ranked contestants

  • Incentive-Compatible: the better you do in competitions, the higher your rating will be

  • Robust Response: one very bad (or very good) event cannot change your rating too much

Cons:

  • new players will take a long time to converge to their skill rating (long time)




3. Trueskill

  • Example: Halo 2 online

  • improves upon ELO















  • Eric is experienced, so his area is tall & thin

  • When Natalia wins, his value will grow taller & thinner (average skill+, uncertainty-)

  • Eric has a low average skill (25), as a result, he will not lose much value on that


Pros:

  • Flexible and can be applied to many different kinds of competitive games

  • quickly converges to the player's true skill (only a few games)

  • easier to model new players (with the initial rating of 0 and uncertainty)

Cons:

  • calculations are very complex, players may feel confused and "unfair"

  • it is proprietary and may need a license (the alternative is the Glicko system - limited to 1v1)



Conclusion:

I found that a lot of the matchmaking and ranking methods are all based on the classic ELO system. As the ELO system was originally designed to support the 1 vs. 1 chess game and our game is a multiplayer party game, we need a matching system that: supports the multiplayer function, can be an incentive - Compatible and a single event may not influence the player’s overall score. At the same time, we would like our players to feel “fair”. As a result, the ELO- MMR can satisfy our needs.

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