Equation Icon  ∑n ∑n (Γ ) = aT ⋅ S ⋅ a = S a a , 𝒜, ℬ = 1,...,m. (72 ) ξξ 𝒜ℬ (𝒜 ℬ) (𝒜ℬ)ij i j i=1 j=1