code: def _calc_tau_2(self, x, loss):
      return loss / (utils.math.norm(x, order=2) ** 2 + 0.5 / self.C)
  
imports: from __future__ import annotations
  import collections
  import numpy
  from river import base, optim, utils
label_desc: Use image node_id 4 for calling the BasePA obj's underlying member method code with example usage: obj._calc_tau_2(x, loss) and returns: unknown