Class: Statistics::Distribution::Normal

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

Direct Known Subclasses

StandardNormal

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(avg, std) ⇒ Normal

Returns a new instance of Normal.



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# File 'lib/statistics/distribution/normal.rb', line 7

def initialize(avg, std)
  self.mean = avg.to_f
  self.standard_deviation = std.to_f
  self.variance = std.to_f**2
end

Instance Attribute Details

#mean ⇒ Object Also known as: mode

Returns the value of attribute mean.



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

def mean
  @mean
end

#standard_deviation ⇒ Object

Returns the value of attribute standard_deviation.



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

def standard_deviation
  @standard_deviation
end

#variance ⇒ Object

Returns the value of attribute variance.



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

def variance
  @variance
end

Instance Method Details

#cumulative_function(value) ⇒ Object 



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# File 'lib/statistics/distribution/normal.rb', line 13

def cumulative_function(value)
  (1/2.0) * (1.0 + Math.erf((value - mean)/(standard_deviation * Math.sqrt(2.0))))
end

#density_function(value) ⇒ Object 



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# File 'lib/statistics/distribution/normal.rb', line 17

def density_function(value)
  return 0 if standard_deviation <= 0

  up_right = (value - mean)**2.0
  down_right = 2.0 * variance
  right = Math.exp(-(up_right/down_right))
  left_down = Math.sqrt(2.0 * Math::PI * variance)
  left_up = 1.0

  (left_up/(left_down) * right)
end