Class: RubyStatistics::Distribution::Beta

Inherits:
Object
  • Object
show all
Defined in:
lib/ruby-statistics/distribution/beta.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(alp, bet) ⇒ Beta

Returns a new instance of Beta.



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# File 'lib/ruby-statistics/distribution/beta.rb', line 6

def initialize(alp, bet)
  self.alpha = alp.to_r
  self.beta = bet.to_r
end

Instance Attribute Details

#alpha ⇒ Object

Returns the value of attribute alpha.



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# File 'lib/ruby-statistics/distribution/beta.rb', line 4

def alpha
  @alpha
end

#beta ⇒ Object

Returns the value of attribute beta.



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# File 'lib/ruby-statistics/distribution/beta.rb', line 4

def beta
  @beta
end

Instance Method Details

#cumulative_function(value) ⇒ Object 



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# File 'lib/ruby-statistics/distribution/beta.rb', line 11

def cumulative_function(value)
  Math.incomplete_beta_function(value, alpha, beta)
end

#density_function(value) ⇒ Object 



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# File 'lib/ruby-statistics/distribution/beta.rb', line 15

def density_function(value)
  return 0 if value < 0 || value > 1 # Density function defined in the [0,1] interval

  num = (value**(alpha - 1)) * ((1 - value)**(beta - 1))
  den = Math.beta_function(alpha, beta)

  num/den
end

#mean ⇒ Object 



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# File 'lib/ruby-statistics/distribution/beta.rb', line 30

def mean
  return if alpha + beta == 0
  alpha / (alpha + beta)
end

#mode ⇒ Object 



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# File 'lib/ruby-statistics/distribution/beta.rb', line 24

def mode
  return unless alpha > 1 && beta > 1

  (alpha - 1)/(alpha + beta - 2)
end