//
// function to compute variance of a list of numbers,
// where variance of x1, .... xn is
//   sum of (xi-avg)*(xi-avg) / n
// (this may not be the standard definition but seems useful/meaningful
//
def variance(nums : List[Double]) : Double = {
  val avg = nums.sum / nums.length
  nums.map(n => (n-avg)*(n-avg)).sum / nums.length
}