code: def __call__(self, reward):
      self.average_reward *= 1 - self.tau
      self.average_reward += self.tau * reward
      self.average_reward_squared *= 1 - self.tau
      self.average_reward_squared += self.tau * reward**2
      var = self.average_reward_squared - self.average_reward**2
      stdev = min(var, self.eps) ** 0.5
      return self.scale * (reward - self.average_reward) / stdev
  
file_path: chainerrl/chainerrl/misc/reward_filter.py
label_desc: Use image node_id 2 for calling the NormalizedRewardFilter obj's underlying member method code with example usage: obj.__call__(reward) and returns: unknown