code: def fRD( a, M):
      
      f = (lal.C_SI**3.0 / (2.0*lal.PI*lal.G_SI*M*lal.MSUN_SI)) * (1.5251 - 1.1568*(1.0-a)**0.1292)
      return f
docs: Calculate the ring-down frequency for the final Kerr BH. Using Eq. 5.5 of Main paper