gistfile1.rb

Math.module_eval do
  def self.variance(population)
    n = 0
    mean = 0.0
    s = 0.0
    population.each do |x|
      n += 1
      delta = x - mean
      mean = mean + (delta / n)
      s = s + delta * (x - mean)
    end
    return s / n
  end
 
  def self.stddev(population)
    Math.sqrt(Math.variance(population)) rescue (0.0/0.0)
  end
end