static double doubleSum(Iterable<Double> l) {
  double sum = 0;
  for (Double i : unnull(l))
    if (i != null) sum += i;
  ret sum;
}

static double doubleSum(double[] l) {
  double sum = 0;
  for (double i : unnull(l))
    sum += i;
  ret sum;
}