Class: Saulabs::TrueSkill::Factors::GreaterThan

Inherits:
Base
  • Object
show all
Defined in:
lib/saulabs/trueskill/factors/greater_than.rb

Instance Method Summary collapse

Methods inherited from Base

#bind, #message_count, #reset_marginals, #send_message_at

Constructor Details

#initialize(epsilon, variable) ⇒ GreaterThan

Returns a new instance of GreaterThan.



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# File 'lib/saulabs/trueskill/factors/greater_than.rb', line 9

def initialize(epsilon, variable)
  super()
  @epsilon = epsilon
  bind(variable) 
end

Instance Method Details

#log_normalization ⇒ Object 



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# File 'lib/saulabs/trueskill/factors/greater_than.rb', line 15

def log_normalization
  msg = @variables[0] / @messages[0]
  -Gauss::Distribution.log_product_normalization(msg, @messages[0]) + 
   Math.log(Gauss::Distribution.cdf((msg.mean - @epsilon) / msg.deviation))
end

#update_message_at(index) ⇒ Object 



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# File 'lib/saulabs/trueskill/factors/greater_than.rb', line 21

def update_message_at(index)
  raise "illegal message index: #{index}" if index < 0 || index > 0
  message = @messages[index]
  variable = @bindings[@messages[index]]
  
  msg = variable / message
  c = msg.precision
  d = msg.precision_mean
  sqrt_c = Math.sqrt(c)
  d_sqrt_c = sqrt_c == 0 ? 0.0 : d / sqrt_c 
  e_sqrt_c = @epsilon * sqrt_c
  denom = 1.0 - Gauss::TruncatedCorrection.w_exceeds_margin(d_sqrt_c, e_sqrt_c)
  new_precision = c / denom
  new_precision_mean = (d + sqrt_c * Gauss::TruncatedCorrection.v_exceeds_margin(d_sqrt_c, e_sqrt_c)) / denom
  new_marginal = Gauss::Distribution.with_precision(new_precision_mean, new_precision)
  new_message = message * new_marginal / variable
  diff = new_marginal - variable
  message.replace(new_message)
  variable.replace(new_marginal)
  return diff
end