code: def get_averaged_interaction(self):
          
  
          # v[triplet, band0, band, band]
          v = self._interaction_strength
          w = self._weights_at_q
          v_sum = np.dot(w, v.sum(axis=2).sum(axis=2))
          return v_sum / np.prod(v.shape[2:])
docs: Return sum over phonon triplets of interaction strength
  
          See Eq.(21) of PRB 91, 094306 (2015)