p (w|i, d) is the language model at position i.
to control the impact of out-ofdocument vocabulary, we add a parameter µ ∈ [0, +∞) here: Analogously, for the positional-based smoothing, the smoothed count by positional proximity is We apply the best positional proximity based density function of Gaussian projection ψ(i, j) in (Lv and Zhai, 2009).