code: def jacobian(self, maps):
          
          mchirp = maps[parameters.mchirp]
          eta = maps[parameters.eta]
          m1 = conversions.mass1_from_mchirp_eta(mchirp, eta)
          m2 = conversions.mass2_from_mchirp_eta(mchirp, eta)
          return mchirp * (m1 - m2) / (m1 + m2)**3
docs: Returns the Jacobian for transforming mchirp and eta to mass1 and
          mass2.