Class: Statistics::Distribution::Binomial

Inherits:
Object
  • Object
show all
Defined in:
lib/statistics/distribution/binomial.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(n, p) ⇒ Binomial

Returns a new instance of Binomial.



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# File 'lib/statistics/distribution/binomial.rb', line 5

def initialize(n, p)
  self.number_of_trials = n.to_i
  self.probability_per_trial = p
end

Instance Attribute Details

#number_of_trials ⇒ Object

Returns the value of attribute number_of_trials.



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# File 'lib/statistics/distribution/binomial.rb', line 4

def number_of_trials
  @number_of_trials
end

#probability_per_trial ⇒ Object

Returns the value of attribute probability_per_trial.



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# File 'lib/statistics/distribution/binomial.rb', line 4

def probability_per_trial
  @probability_per_trial
end

Instance Method Details

#cumulative_function(k) ⇒ Object 



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# File 'lib/statistics/distribution/binomial.rb', line 18

def cumulative_function(k)
  return if k < 0 || k > number_of_trials
  k = k.to_i

  p = 1 - probability_per_trial
  Math.incomplete_beta_function(p, number_of_trials - k, 1 + k)
end

#mean ⇒ Object 



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# File 'lib/statistics/distribution/binomial.rb', line 26

def mean
  number_of_trials * probability_per_trial
end

#mode ⇒ Object 



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# File 'lib/statistics/distribution/binomial.rb', line 34

def mode
  test = (number_of_trials + 1) * probability_per_trial

  returned = if test == 0 || (test % 1 != 0)
               test.floor
             elsif (test % 1 == 0)  && (test >= 1 && test <= number_of_trials)
               [test, test - 1]
             elsif test == number_of_trials + 1
               number_of_trials
             end

  returned
end

#probability_mass_function(k) ⇒ Object 



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# File 'lib/statistics/distribution/binomial.rb', line 10

def probability_mass_function(k)
  return if k < 0 || k > number_of_trials
  k = k.to_i

  Math.combination(number_of_trials, k) *
    (probability_per_trial ** k) * ((1 - probability_per_trial) ** (number_of_trials - k))
end

#variance ⇒ Object 



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# File 'lib/statistics/distribution/binomial.rb', line 30

def variance
  mean * (1 - probability_per_trial)
end