  Neutron-proton elliptic flow difference and ratio have been shown to be
promising observables in the attempt to constrain the density dependence of the
symmetry energy above the saturation point from heavy-ion collision data. Their
dependence on model parameters like microscopic nucleon-nucleon cross-sections,
compressibility of nuclear matter, optical potential, and symmetry energy
parametrization is thoroughly studied. By using a parametrization of the
symmetry energy derived from the momentum dependent Gogny force in conjunction
with the T\"{u}bingen QMD model and comparing with the experimental FOPI/LAND
data for 197Au+197Au collisions at 400 MeV/nucleon, a moderately stiff, x=-1.35
+/- 1.25, symmetry energy is extracted, a result that agrees with that of a
similar study that employed the UrQMD transport model and a momentum
independent power-law parametrization of the symmetry energy. This contrasts
with diverging results extracted from the FOPI $\pi^{-}/\pi^{+}$ ratio
available in the literature.
