The symmetry potential has the form

\[ U_{Sym} = \pm 2 S_{pot} \frac{I_3}{I} \frac{\rho_{I_3}}{\rho_0} + S(\rho_B)\left(\frac{\rho_{I_3}}{\rho_B}\right)^2 \,, \]

where \( \rho_{I_3}\) is the density of the relative isospin \( I_3/I \) and \( \rho_B \) is the net baryon density.

S_pot (double, required, no default):
Parameter \(S_{pot}\) of symmetry potential in MeV

gamma (double, no default):
Power \( \gamma \) in formula for \( S(\rho_B) \):

\[ S(\rho_B)=12.3\,\mathrm{MeV}\times \left(\frac{\rho_B}{\rho_0}\right)^{2/3}+ 20\,\mathrm{MeV}\times\left(\frac{\rho_B}{\rho_0}\right)^\gamma \]

If gamma is specified, the baryon density dependence is included in the potential. Otherwise only the first term of the potential will be taken into account.