lib/exonio/financial.rb
def irr(values)
      func = Helpers::IrrHelper.new(values)
      guess = [ func.eps ]
      nlsolve( func, guess)
      guess[0]
    end
def irr(values)
      func = Helpers::IrrHelper.new(values)
      guess = [ func.eps ]
      nlsolve( func, guess)
      guess[0]
    end
Calculates the internal rate of return on an investment based on a
 series of periodic cash flows.

 @param cashflows [Array] An array containing the income or payments
 associated with the investment

 @return [Float]

 @example
   Exonio.irr([-100, 39, 59, 55, 20]) # ==> 0.28094842116...