Equation Icon  ∑N f(xb) ⟨f(xa)⟩ = ξ(xa) -------Ωab, (89 ) b=1 ⟨n(xb)⟩ ∑N f(x ) ⟨∇f (xa)⟩ = ξ(xa) ----b--∇xa Ωab, (90 ) b=1 ⟨n(xb)⟩ ∑N A (x ) ⟨∇ ⋅ A (xa)⟩ = ξ(xa) -----b-⋅ ∇xaΩab, (91 ) b=1 ⟨n(xb)⟩