Class: Olympic::Rating::Glicko::Formula

Inherits:
Object
  • Object
show all
Extended by:
Memoist
Defined in:
lib/olympic/rating/glicko/formula.rb

Constant Summary collapse

DEFAULT_RATING =

The default rating. Glicko states to use 1500 as the default.

1500
DEFAULT_RATING_DERIVATION =

The default RD. Glicko states to use 350 as the default.

350
CERTAINTY_DECAY =

This is the “certainty decay,” or the constant value that is used in Step 1 of the Glicko rating system. It denotes the decay of certainty of a player’s rating over a given time (see Olympic::Rating::Glicko for a definition of time). The default chosen here expects a typical RD of 50, with 10 time units before a decay to 350. The formula would be (in LaTeX):

c = \sqrt{\frac{350^2-50^2}{10}}

However, in order to optimize operations, this is c^2. So the actual value of this would be:

c = \frac{350^2-50^2}{10}

12_000
Q = 
Math.log2(10).fdiv(400)
Q2 = 
Q ** 2

Instance Method Summary collapse

Constructor Details

#initialize(unit, matches) ⇒ Formula

Returns a new instance of Formula.



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# File 'lib/olympic/rating/glicko/formula.rb', line 35

def initialize(unit, matches)
  @unit = unit
  @matches = matches
end

Instance Method Details

#call ⇒ Object 



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# File 'lib/olympic/rating/glicko/formula.rb', line 40

def call
  flush_cache
  @unit.rating = new_rating
  @unit.derivation = new_derivation
end

#derivation ⇒ Numeric

This returns the current rating derivation of the unit. It clamps the rating derivation to between 30 and 350. The Glicko system states that it must be less than or equal to 350, but later recommends not letting the rating derivation drop below 30.

Returns:

  • (Numeric) 


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# File 'lib/olympic/rating/glicko/formula.rb', line 53

def derivation
  if @unit.unrated?
    350
  elsif @unit.time_passed == 0
    @unit.derivation
  else
    a = [
      30,
      Math.sqrt((@unit.derivation) ** 2 + CERTAINTY_DECAY * @unit.time_passed),
      350
    ].sort[1]
  end
end