static double smoothedMovingAverage(double period, double... a) {
  int n = l(a);
  if (n == 0) ret Double.NaN;
  double alpha = reciprocal(period);
  double value = first(a);
  for (int i = 1; i < n; i++)
    value = blend(value, a[i], alpha);
  ret value;
}

Began life as a copy of #1010188