The class is libLSS/physics/bias/many_power.hpp, class is LibLSS::bias::ManyPower.

This class implements the linear bias model. Its corresponding mathematical model is given by the quadratic form {$$N_g = V^T Q V,$$} with {$$V_i = (\delta_m^{ (a_i) })^{k_i},$$} with {$k_i$} being an arbitrary positive integer, depending on the index {$i$}, {$\delta^{(a)}_m$} the matter field averaged at scale {$(a)$}.