code: def _constraint(self, params):
          
  
          # ensure that mass1 > mass2
          if params["mass1"] < params["mass2"]:
              return False
  
          # constraint for secondary mass
          a = ((4.0 * params["q"]**2 + 3.0 * params["q"])
                   / (4.0 + 3.0 * params["q"]) * params["xi2"])**2
          b = ((1.0 + params["q"]**2) / 4.0
                   * (params["chi_eff"] + params["chi_a"])**2)
          if a + b > 1:
              return False
  
          # constraint for primary mass
          a = params["xi1"]**2
          b = ((1.0 + params["q"])**2 / (4.0 * params["q"]**2)
                   * (params["chi_eff"] - params["chi_a"])**2)
          if a + b > 1:
              return False
  
          return True
docs: Evaluates constraint function.