class Statistics::Distribution::Binomial

Attributes

number_of_trials[RW]
probability_per_trial[RW]

Public Class Methods

new(n, p) click to toggle source
# 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

Public Instance Methods

cumulative_function(k) click to toggle source
# 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() click to toggle source
# File lib/statistics/distribution/binomial.rb, line 26
def mean
  number_of_trials * probability_per_trial
end
mode() click to toggle source
# 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) click to toggle source
# 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() click to toggle source
# File lib/statistics/distribution/binomial.rb, line 30
def variance
  mean * (1 - probability_per_trial)
end