This parameter is specific to a set of simulations performed to evaluate the efficiency of planet trapping at a cavity edge. Unless you want to reproduce these simulations, you should simply ignore this variable. If you use it, you also have to define
CavityRadius and
CavityWidth.
CavityRatio is the target surface density ratio of the outer to the inner disk. Outside of the cavity (r >
CavityRadius), the surface density profile is whatever is given by
Sigma0 and
SigmaSlope, while inside the cavity it corresponds to this profile divided by
CavityRatio. Similarly, outside the cavity the viscosity is whatever is prescribed by
Viscosity or
AlphaViscosity, while inside the cavity it corresponds to either value multiplied by
CavityRatio.