Module: Random::Testing

Defined in:
lib/random/testing.rb

Overview

Methods related to testing randomness

Class Method Summary collapse

Class Method Details

.chi_square_statistic(binCounts) ⇒ Object

Calculate the chi square statistic for the counts for each bin given in binCounts (an Array of integers).



25
26
27
28
29
30
31
32
33
34
 
# File 'lib/random/testing.rb', line 25

def self.chi_square_statistic(binCounts)
  num_bins = binCounts.length
  sum = binCounts.inject(0) {|s,e| s+e}
  expected = sum.to_f / num_bins
  # puts("Expected = #{expected}")
  binCounts.inject(0) do |chisq, observed|
    d = observed - expected
    chisq + ((d * d) / expected)
  end
end

.chi_square_test(distribution, alpha = 0.01) ⇒ Object

Perform the Chi Square test at a given alpha level. Returns true iff the given distribution can be assumed to come from a uniform distribution at an alpha level of confidence.



10
11
12
13
14
15
16
17
18
19
20
21
 
# File 'lib/random/testing.rb', line 10

def self.chi_square_test(distribution, alpha = 0.01)
  labels, counts = distribution.keys, distribution.values
  degrees_of_freedom = labels.length - 1
  chisq = chi_square_statistic(counts)
  # puts("ChiSq statistic = %.4f" % chisq)
  # puts("Degrees of freedom = #{degrees_of_freedom}")
  critical_chi_square_value = 
    Math::Statistics.critical_chi_square_value(degrees_of_freedom, alpha)
  # If the calculated chi-square statistic is less than the critical value
  # we accept the distribution as coming from a uniform process.
  chisq < critical_chi_square_value
end