code: def lm_deltaf(damping_times, modes):
      
  
      df = {}
      for lmn in modes:
          l, m, nmodes = int(lmn[0]), int(lmn[1]), int(lmn[2])
          for n in range(nmodes):
              df['%d%d%d' %(l,m,n)] = \
                  1. / qnm_time_decay(damping_times['%d%d%d' %(l,m,n)], 1./1000)
  
      return min(df.values())
docs: Return the minimum delta_f of all the modes given, with delta_f given by
      the inverse of the time at which the amplitude of the ringdown falls to
      1/1000 of the peak amplitude.