Class: Glicko2::Rater

Inherits:
Object
  • Object
show all
Defined in:
lib/glicko2/rater.rb

Overview

A Rater calculates a new Rating based on actual game outcomes.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(rating) ⇒ Rater

Returns a new instance of Rater.



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# File 'lib/glicko2/rater.rb', line 6

def initialize(rating)
  @rating = rating
  @v_pre = 0.0
  @delta_pre = 0.0
end

Instance Attribute Details

#rating ⇒ Object (readonly)

Returns the value of attribute rating.



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# File 'lib/glicko2/rater.rb', line 4

def rating
  @rating
end

Instance Method Details

#add(other_rating, score) ⇒ Object

Add an outcome against the rating



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# File 'lib/glicko2/rater.rb', line 13

def add(other_rating, score)
  g, e = other_rating.gravity_expected_score(rating.mean)
  @v_pre += g**2 * e * (1 - e)
  @delta_pre += g * (score - e)
end

#rate(tau) ⇒ Object

Rate calculates Rating as at the start of the following period based on game outcomes



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# File 'lib/glicko2/rater.rb', line 20

def rate(tau)
  v = @v_pre**-1
  delta2 = (@delta_pre * v)**2
  sd2 = rating.sd**2
  a = Math.log(rating.volatility**2)
  if v.finite?
    f = lambda do |x|
      expX = Math.exp(x)
      (expX * (delta2 - sd2 - v - expX)) / (2 * (sd2 + v + expX)**2) - (x - a) / tau**2
    end
    if delta2 > sd2 + v
      b = Math.log(delta2 - sd2 - v)
    else
      k = 1
      k += 1 while f.call(a - k * tau) < 0
      b = a - k * tau
    end
    a = Util.illinois_method(a, b, &f)
  end
  volatility = Math.exp(a / 2.0)
  sd_pre = Math.sqrt(sd2 + volatility**2)
  sd = 1 / Math.sqrt(1.0 / sd_pre**2 + 1 / v)
  mean = rating.mean + sd**2 * @delta_pre
  Rating.new(mean, sd, volatility)
end