code: def secondary_spin(mass1, mass2, spin1, spin2):
      
      mass1, mass2, spin1, spin2, input_is_array = ensurearray(
          mass1, mass2, spin1, spin2)
      ss = copy.copy(spin2)
      mask = mass1 < mass2
      ss[mask] = spin1[mask]
      return formatreturn(ss, input_is_array)
docs: Returns the dimensionless spin of the secondary mass.