Class: Prubybility::Binomial

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

Overview

A representation of the Binomial probability distribution.

See README for example usages.

Direct Known Subclasses

Bernoulli

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(number_of_trials, theta) ⇒ Binomial

Returns a new instance of Binomial.



12
13
14
15
16
17
 
# File 'lib/prubybility/binomial.rb', line 12

def initialize(number_of_trials, theta)
  @n = number_of_trials
  @theta = theta.to_d
  @expected_value = @n * @theta
  @variance = @n * @theta * (1 - @theta)
end

Instance Attribute Details

#expected_value ⇒ Object Also known as: mean

Returns the value of attribute expected_value.



8
9
10
 
# File 'lib/prubybility/binomial.rb', line 8

def expected_value
  @expected_value
end

#n ⇒ Object

Returns the value of attribute n.



8
9
10
 
# File 'lib/prubybility/binomial.rb', line 8

def n
  @n
end

#theta ⇒ Object

Returns the value of attribute theta.



8
9
10
 
# File 'lib/prubybility/binomial.rb', line 8

def theta
  @theta
end

#variance ⇒ Object

Returns the value of attribute variance.



8
9
10
 
# File 'lib/prubybility/binomial.rb', line 8

def variance
  @variance
end

Instance Method Details

#p(number_of_successes) ⇒ Object 



19
20
21
22
 
# File 'lib/prubybility/binomial.rb', line 19

def p(number_of_successes)
  return unless valid_value?(number_of_successes)
  choose(number_of_successes) * (theta**number_of_successes) * ((1 - theta)**(n - number_of_successes))
end