code: def _exponential_kamb(cos_dist, sigma=3):
      
      n = float(cos_dist.size)
      f = 2 * (1.0 + n / sigma**2)
      count = np.exp(f * (cos_dist - 1))
      units = np.sqrt(n * (f/2.0 - 1) / f**2)
      return count, units
docs: Kernel function from Vollmer for exponential smoothing.