code: def _get_population(self, freq, t):  # freq in THz
          
          condition = t > 1.0
          if type(condition) == bool or type(condition) == np.bool_:
              if condition:
                  return 1.0 / (np.exp(freq * THzToEv / (Kb * t)) - 1)
              else:
                  return 0.0
          else:
              vals = np.zeros(len(t), dtype='double')
              vals[condition] = 1.0 / (
                  np.exp(freq * THzToEv / (Kb * t[condition])) - 1)
              return vals
docs: Return phonon population number
  
          Three types of combinations of array inputs are possible.
          - single freq and single t
          - single freq and len(t) > 1
          - len(freq) > 1 and single t