def Pgas(rho,T,mu):
R = old_div(boltzmann_constant, atomic_mass_unit)<EOL>return (old_div(R,mu)) * rho * T<EOL>
P = R/mu * rho * T

Parameters
----------
mu : float
    Mean molecular weight
rho : float
    Density [cgs]
T : float
    Temperature [K]