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# Glicko ratings

Version 3 of SoL introduced a management of players ratings following the Glicko system, mainly to get rid of the random component when generating the first round pairing in important tourneys.

To put it simply, the system computes a rate of each player that represent the mutual probability of victory: a player rated 2200 will most probably win a match against a player rated 1700.

When a tourney is associated to a particular Glicko rating, the round generation algorithm takes into account the current rate of each player.

## Menu actions

In addition to the standard actions the menu at the top contains the following items:

Tourneys
  Opens the management of the tourneys associated with the selected rating
Players
  Opens the rates of the players of the selected rating
Recompute
  Recompute the whole rating, elaborating all the results of all the tourneys associated with the selected rating
Download
  Download an archive of all the tourneys associated with the selected rating

## Insert and edit

Each rating has a description that must be unique, i.e. it is not possible to insert two distinct ratings with the same description.

The level represent the importance of the rating and its dependability.

If inherit is active, then the rate of a player playing in a tourney associated with a particular rating is his most recent rate in the referenced rating or one with an higher level. When it is not active, the search is limited exclusively to the referenced rating.

The tau is the primary coefficient that drives the computation in the Glicko2 algorithm.

The rate, the deviation and the volatility are the default values of the rate of a player at his first tourney with the given rating.

The match outcomes determines the formula used to compute the outcomes of a match and may be set to one of the following values:

`Standard Glicko`

  this is included only for historical reasons and should not be used because it does not fit Carrom very well:

`Guido's formula`

  this is the formula Guido Truffelli tailored on Carrom characteristics, approved by dr. Glickman himself:

`Exponential on scores difference`

  this is an attempt to take into account the score difference, so that a player gets a better outcome if he wins by `20—15` rather than by `4—3`:

The lower points and higher points values are used to interpolate the rate of debut players (i.e. players who do not carry a previous rate), when there are less than two already rated players. This happens in particular for the first tourney of a new rating, expecially if inherit is not active.

Important

Only the system administrator is allowed to change these values: usually they should not be modified.

In any case, when these values get changed the rating should be recomputed.

The responsible is usually the user that inserted that particular rating: the information related to the rating are changeable only by him (and also by the administrator of the system).

## Historical ratings

Historical ratings may be loaded with the `soladmin load-historical-rating` command line tool that accepts the following options and requires two positional arguments, respectively the configuration file and an URL of the file containing the historical ratings:

`--date` | Bogus rates date, by default 1900-01-01
`--deviation` | Value of the deviation, by default 100, or a formula to compute it from other fields
`--volatility` | Value of the volatility, by default 0.006, or a formula to compute it from other fields
`--rate` | Formula to compute the player’s rate, if the value in the file needs to be adjusted
`--description` | Description of the historical rating
`--level` | The level of the rating, 0 by default: 0=historical, 1=international, 2=national, 3=regional, 4=courtyard
`--inherit` | Whether player’s rate will be inherited from other ratings at the same level or better, False by default
`--map` | Specify a map between internal (SoL) field name and external one
`--encoding` | Encoding of the CSV file, by default UTF-8
`--tsv` | Fields are separated by a TAB, not by a comma
`--dry-run` | Just show the result, do not actually insert data

The data file may be specified either as an URL like `http://hostname.com/path/to/data.txt` or as a local file with `file:///tmp/data.txt`.

The specified text file must contain either comma-separated-values or tab-separated-values (if the option `--tsv` is given) lines. If not otherwise specified with the option `--encoding` it is loaded as an UTF-8 stream.

The first row is considered as the header that specifies the names of each column and the remaining rows are considered the real data, each one containing the value of the rate of a single player.

Any single row must contain at least the fields `firstname`, `lastname` and `nickname` to univocally identify a particular player, and optionally his `sex` and the `club` he plays for. There must obviously be the `rate` field containing the actual value of his historical rate. These are the internal names of the fields, but with the option `--map` you can specify an arbitrary mapping to the actual names used in the file.

As an example, the following data

    id,surname,firstname,nickname,rating,matches_played,club,sex
    1,Gaifas,EMANUELE,,1000,30,,Scarambol Club Rovereto,M
    2,ROSSI,PAOLO,,1468,6,Scarambol Club Rovereto,M
    3,Verdi,Giuseppe,,1427,34,Italian Carrom Federation,M
    4,Bianchi,Stefania,,1495,7,,F

may be loaded with the following command:

    soladmin load-historical-rating \
             --map lastname=surname \
             --map rate=rating \
             --map matches_played=matches_played \
             --map club \
             --map sex \
             --deviation "350.0 / (10.0 - 9.0*exp(-matches_played / 60.0))" \
             --description "Historical rating" \
             --dry-run \
             config.ini /tmp/players.csv

that should produce something like the following output:

    Loading ratings from file:///tmp/players.csv...
    Gaifas Emanuele “lele” (Scarambol Club Rovereto): rate=1000 deviation=77 volatility=0.006
    NEW Rossi Paolo (Scarambol Club Rovereto): rate=1468 deviation=188 volatility=0.006
    NEW Verdi Giuseppe (Italian Carrom Federation): rate=1427 deviation=71 volatility=0.006
    NEW Bianchi Stefania (None): rate=1495 deviation=175 volatility=0.006

where you can see that:

1. the `--dry-run` option just shows what would happen, without altering the database
2. player’s names are normalized, that is `EMANUELE` becomes `Emanuele`
3. new players are automatically added to the database
4. the deviation value is computed from the number of played matches

When you are satisfied, omit the `--dry-run` option and the data will be effectively loaded.

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