class MoreMath::Sequence

def harmonic_mean

is less than or equal to 0.0, this method returns NaN.
Returns the harmonic mean of the elements. If any of the elements 
def harmonic_mean
  sum = @elements.inject(0.0) { |s, t|
    if t > 0
      s + 1.0 / t
    else
      break nil
    end
  }
  sum ? size / sum : 0 / 0.0
end