Here is are four explanations of how ratings are computed for newcomers (players who do nothave a previous rating) at a tournament,in order of increasing accuracy and technical detail. Questions should
be directed to [[John Chew]].
== Overview ==
A newcomer’s initial rating is the rating s/he
would have had to have had in order for his/her rating
to have remained unchanged after their first tournament.
== Summary ==
If there is only one newcomer in a division,
then the newcomer receives an initial rating
equal to their performance rating (the rating
the newcomer would have had to have had before
the event in order for it to have remained
unchanged), except that an initial rating may
never be less than 500, and it may
not exceed a newcomer’s strongest opponent’s
rating by more than 400 times the newcomer’s
winning percentage.
If there is more than one newcomer, then they are
assigned provisional ratings equal to their average
opponent rating, which are then repeatedly replaced
by their performance ratings until the ratings
stablise.
== Pseudocode ==
*'''For each''' rated player ''rp''
**'''For each''' newcomer ''nc''
***'''Set''' ''nc''’s ''new rating'' to the mean of ''nc''’s last 50 ''iterative ratings''
== Reference implementation ==
The reference implementation of the rating algorithm is
in Perl and can be found as part of the
[http://www.math.utoronto.ca/jjchew/software/tsh/lib/perl/Ratings/Elo.pm tsh software distribution]
in the Ratings::Elo::RateNewcomersCorrectly() method.