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horaceho/ers
============

EGF Rating System

1.0.4(2y ago)122MITPHPPHP >=7.0

Since Oct 26Pushed 2y ago1 watchersCompare

[ Source](https://github.com/horaceho/ers)[ Packagist](https://packagist.org/packages/horaceho/ers)[ RSS](/packages/horaceho-ers/feed)WikiDiscussions master Synced today

READMEChangelog (3)DependenciesVersions (6)Used By (0)

ERS (EGF Rating System)
=======================

[](#ers-egf-rating-system)

The rating algorithm was updated starting 2021. The whole database from back in 1996 was recalculated with this algorithm. You can find the old algorithm here.

- Ratings are updated by: `r' = r + con * (Sa - Se) + bonus`
- `r` is the old EGD rating (GoR) of the player
- `r'` is the new EGD rating of the player
- `Sa` is the actual game result (1.0 = win, 0.5 = jigo, 0.0 = loss)
- `Se` is the expected game result as a winning probability (1.0 = 100%, 0.5 = 50%, 0.0 = 0%). See further below for its computation.
- `con` is a factor that determines rating volatility (similar to K in regular Elo rating systems): `con = ((3300 - r) / 200) ^ 1.6`
- `bonus` (not found in regular Elo rating systems) is a term included to counter rating deflation: `bonus = ln(1 + exp((2300 - rating) / 80)) / 5`
- `Se` is computed by the Bradley-Terry formula: `Se = 1 / (1 + exp(β(r2) - β(r1)))`
- `r1` is the EGD rating of the player
- `r2` is the EGD rating of the opponent
- `β` is a mapping function for EGD ratings: `β = -7 * ln(3300 - r)`

[EGF Official ratings system](https://www.europeangodatabase.eu/EGD/EGF_rating_system.php)

Usage
-----

[](#usage)

```
composer require horaceho/ers
```

```