Class: Binomial::Calculator

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

Overview

Params:

- trials:         Total number of trials conducted
- probability:    The probability of one success
- target:         The desired amount of successes

Direct Known Subclasses

CumulativeCalculator

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(params = {}) ⇒ Calculator

Returns a new instance of Calculator.



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# File 'lib/binomial/calculator.rb', line 10

def initialize(params = {})
  @trials = params[:trials]
  @probability = params[:probability]
  @target = params[:target]

  check_positive(:@trials)
  check_positive(:@target)
  check_positive(:@probability)

  @probability <= 1  or raise "Error: probability[#{@probability}] must be <= 1"
  @trials >= @target or raise "Error: target[#{@target}] must be < trials[#{@trials}]"
end

Instance Attribute Details

#probability ⇒ Object

Returns the value of attribute probability.



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# File 'lib/binomial/calculator.rb', line 8

def probability
  @probability
end

#target ⇒ Object

Returns the value of attribute target.



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# File 'lib/binomial/calculator.rb', line 8

def target
  @target
end

#trials ⇒ Object

Returns the value of attribute trials.



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# File 'lib/binomial/calculator.rb', line 8

def trials
  @trials
end

Instance Method Details

#calculate ⇒ Object

Calculates the result



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# File 'lib/binomial/calculator.rb', line 41

def calculate
  @trials.choose(@target) *
  (@probability ** @target) *
  ((1 - @probability) ** (@trials - @target))
end

#check_positive(inst_var) ⇒ Object

param: name of instance variable WITH leading @



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# File 'lib/binomial/calculator.rb', line 24

def check_positive(inst_var)
  value = instance_variable_get(inst_var)
  var_name = inst_var.to_s.delete('@')
  value > 0 or
    raise "Error: '#{var_name}' must be > 0, but was: #{value}"
end

#equation ⇒ Object

A representation of the equation performed



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# File 'lib/binomial/calculator.rb', line 36

def equation
  "P(X=#{@target}) = #{@trials}C#{@target} * #{@probability}^#{@target} * #{1 - @probability}^#{@trials - @target} = #{calculate}"
end

#model ⇒ Object 



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# File 'lib/binomial/calculator.rb', line 31

def model
  "X~B(#{@trials}, #{@probability})"
end