code: def _constraints(self, values):
          
          mass1, mass2, phi_a, phi_s, chi_eff, chi_a, xi1, xi2, _ = \
              conversions.ensurearray(values['mass1'], values['mass2'],
                                      values['phi_a'], values['phi_s'],
                                      values['chi_eff'], values['chi_a'],
                                      values['xi1'], values['xi2'])
          s1x = conversions.spin1x_from_xi1_phi_a_phi_s(xi1, phi_a, phi_s)
          s2x = conversions.spin2x_from_mass1_mass2_xi2_phi_a_phi_s(mass1, mass2,
              xi2, phi_a, phi_s)
          s1y = conversions.spin1y_from_xi1_phi_a_phi_s(xi1, phi_a, phi_s)
          s2y = conversions.spin2y_from_mass1_mass2_xi2_phi_a_phi_s(mass1, mass2,
              xi2, phi_a, phi_s)
          s1z = conversions.spin1z_from_mass1_mass2_chi_eff_chi_a(mass1, mass2,
              chi_eff, chi_a)
          s2z = conversions.spin2z_from_mass1_mass2_chi_eff_chi_a(mass1, mass2,
              chi_eff, chi_a)
          test = ((s1x**2. + s1y**2. + s1z**2.) < 1.) & \
                 ((s2x**2. + s2y**2. + s2z**2.) < 1.)
          return test
docs: Applies physical constraints to the given parameter values.
  
          Parameters
          ----------
          values : {arr or dict}
              A dictionary or structured array giving the values.
  
          Returns
          -------
          bool
              Whether or not the values satisfy physical