Glicko

A Unity C# implementation of the Glicko-2 player rating system sourced from @TaylorP in his C++ implementation TaylorP/Glicko2. Glicko and Glicko-2 are alternatives to traditional Elo rating systems. Glicko was developed by Mark Glickman; the theoretical details of the system is described on Dr. Glickman's website. Both the original Glicko and Glicko-2 rating systems are in the public domain.

Usage

The rating system has two components: the configuration and rating objects. The values in Glicko described all of the configurable components and can be changed in the project settings in Edit -> ProjectSettings/CondorHalcon/Glicko; this includes the default rating values and system constants. Details of how to configure the rating system are described in the Glicko-2 paper.

New ratings can be created as follows:

    // Create a new Rating instance with the default rating
    Rating rating = new Rating(Glicko.DefaultRating);

    // Create a new Rating instance with a specific rating
    Rating rating = new Rating(1500);

    // Create a new Rating instance with a specific rating and deviation
    Rating rating = new Rating(1500, 200);

    // Create a new Rating instance with a specific rating, deviation and volatility
    Rating rating = new Rating(1500, 310, 0.04)

In the Glicko rating system, player ratings are updated in batches. As described in the Glicko-2 paper, the ideal number of games in a rating period is 10-15. As such, the primary method for updating a rating is the Rating.Update() method. This arguments to the Rating.Update() method are a game count, an array of opponent ratings and the outcome of the games. As per the Glicko-2 paper, a victor has the score 1.0, a draw is scored as 0.5 and a loss is 0.0.

For example:

    // The test player
    Rating player = new Rating(1500, 200);

    // The three opponents
    Rating opponent1 = new Rating(1400, 30);
    Rating opponent2 = new Rating(1550, 100);
    Rating opponent3 = new Rating(1700, 300);

    // Update the ratings from the 3 games
    Match[] matches = new Match[]{ new Match(opponent1, 1.0), new Match(opponent2, 0), new Match(opponent3, 0)};
    player.Update(matches);
    player.Apply();

A version of Rating.Update() that takes a single opponent and game outcome can also be used. This method is useful in situations where the ratings are updated with each game, such as an online chess environment:

    // Player1's rating
    Rating player1 = new Rating(1500, 200);

    // Player2's rating
    Rating player2 = new Rating(1400, 30);

    // Update the ratings based on a game in which player1 beat player2
    player1.Update(new Match(player2, 1.0));
    player2.Update(new Match(player1, 0.0));

    player1.Apply();
    player2.Apply();

If a player does not play any games during a rating period, the Glicko-2 document recommends that their rating deviation is updated based on the volatility, as described in Step 6 of the Glicko pdf. This can be achieved using the Rating.Decay() function:

    player.Decay()

After calling Rating.Update() or Rating.Decay(), the changes must be applied using the Rating.Apply() method. This is necessary because updates to multiple Rating instances may depend on each other and ratings should be not updated until all outcomes have been processed.

    player.Apply();

License

This implementation of the Glicko-2 rating system is distributed under The MIT License.