code: def inverse_transform(self, maps):
          
          mass1 = maps[parameters.mass1]
          spin1z = maps[parameters.spin1z]
          mass2 = maps[parameters.mass2]
          spin2z = maps[parameters.spin2z]
          out = {
              parameters.chi_eff : conversions.chi_eff(mass1, mass2,
                                                       spin1z, spin2z),
              "chi_a" : conversions.chi_a(mass1, mass2, spin1z, spin2z),
          }
          return self.format_output(maps, out)
docs: This function transforms from component masses and cartesian spins
          to mass-weighted spin parameters aligned with the angular momentum.
  
          Parameters
          ----------
          maps : a mapping object
  
          Returns
          -------
          out : dict
              A dict with key as parameter name and value as numpy.array or float
              of transformed values.