Class: Prubybility::NegativeBinomial

Inherits:
Object
  • Object
show all
Includes:
Combinations
Defined in:
lib/prubybility/negative_binomial.rb

Overview

A representation of the Negative Binomial probability distribution.

See README for example usages.

Direct Known Subclasses

Geometric

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Combinations

choose

Constructor Details

#initialize(fixed_successes, theta) ⇒ NegativeBinomial 



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# File 'lib/prubybility/negative_binomial.rb', line 14

def initialize(fixed_successes, theta)
  @k = fixed_successes
  @theta = theta.to_d
  @expected_value = @k / @theta
  @variance = @k / @theta * (1 / @theta - 1)
end

Instance Attribute Details

#expected_value ⇒ Object Also known as: mean

Returns the value of attribute expected_value.



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# File 'lib/prubybility/negative_binomial.rb', line 10

def expected_value
  @expected_value
end

#k ⇒ Object

Returns the value of attribute k.



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# File 'lib/prubybility/negative_binomial.rb', line 10

def k
  @k
end

#theta ⇒ Object

Returns the value of attribute theta.



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# File 'lib/prubybility/negative_binomial.rb', line 10

def theta
  @theta
end

#variance ⇒ Object

Returns the value of attribute variance.



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# File 'lib/prubybility/negative_binomial.rb', line 10

def variance
  @variance
end

Instance Method Details

#p(var) ⇒ Object 



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# File 'lib/prubybility/negative_binomial.rb', line 21

def p(var)
  choose(var) * (theta**k) * ((1 - theta)**(var - k))
end