Cosine Similarity

¡ If X and Y are two n- dimensional vectors: X · Y = |X| |Y| cos θ cos θ = X · Y / |X| |Y| = 1 when identical = 0 when orthogonal

Cos (Q,Dd)   = Q · Dd / |Q| |Dd|        = (1/WqWd) Σ wq,t · wd,t        = (1/Wd) Σ wq,t · wd,t