class MathProbability::Probability

This class encapsulates mathimatical probability methods.

Public Class Methods

combinations(objects, at_a_time) click to toggle source
# File lib/math_probability.rb, line 26
def self.combinations(objects, at_a_time)
  (((objects.factoral)/((objects-at_a_time).factoral))*(1.0/(at_a_time.factoral))).to_i
end
permutations_no_repeat(objects, at_a_time) click to toggle source
# File lib/math_probability.rb, line 18
def self.permutations_no_repeat(objects, at_a_time)
  (objects.factoral)/(objects - at_a_time).factoral
end
permutations_with_repeat(objects, at_a_time) click to toggle source
# File lib/math_probability.rb, line 22
def self.permutations_with_repeat(objects, at_a_time)
  objects**at_a_time
end
probability(choices, outcomes, reduce=true) click to toggle source
# File lib/math_probability.rb, line 30
def self.probability(choices, outcomes, reduce=true)
  a = choices.to_f / outcomes
  answer = {decimal: a, percentage: "#{a*100}%", fraction: (reduce ? reduced_fraction(choices, outcomes) : "#{choices}/#{outcomes}")}
end
sigma(start_seq, end_seq, seq_step) click to toggle source
# File lib/math_probability.rb, line 8
def self.sigma(start_seq, end_seq, seq_step)
  summnation ||= 0
  seq_step.gsub!(/((?![x-z0-9\s\.\-\+\*\/\(\)]).)*/,'').upcase!
  raise ArgumentError , "Only use x,y,z as variables" if (seq_step =~ /[A-Z]/).nil?
  (start_seq..end_seq).each do |value|
    summnation += eval(seq_step.gsub(/[X-Z]/,value.to_s))
  end
  summnation
end

Private Class Methods

reduced_fraction(nominator, denominator) click to toggle source
# File lib/math_probability.rb, line 37
def self.reduced_fraction(nominator, denominator)
  lcd ||= denominator
  denominator.downto(2).each do |n|
    if nominator % n == 0 && denominator % n == 0 && n != denominator && n < lcd
      lcd = n
    end
  end
  lcd != denominator ? "#{nominator/lcd}/#{denominator/lcd}" : "#{nominator}/#{denominator}"
end