code: def _get_stddevs(self, C, distance, stddev_types):
          
          stddevs = []
          for stddev_type in stddev_types:
              assert stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
              if stddev_type == const.StdDev.TOTAL:
                  sigma = C["s1"] + (C["s2"] / (1.0 +
                                     ((distance / C["s3"]) ** 2.)))
                  stddevs.append(sigma + np.zeros_like(distance))
          return stddevs
docs: Returns the total standard deviation, which is a function of distance