The model implemented in ARES is the most simple 'linear' model. The density field is supposed to be a pure Gaussian random field, which linearly biased, selected and with a Gaussian error model. For a single catalog, the forward model corresponds to:
\tag{1} N^\mathrm{g}_p = \bar{N} R_p (1 + b \delta_p) + n_p
with \langle n_p n_{p'} \rangle = R_p \bar{N} \delta^K_{p, p'},