Mean functions

KronMean(A, X)	Kronecker mean function, (A⊗X)vec(B).
LinearMean(X)	Linear mean function, X𝜶.
OffsetMean(n)	Offset mean function, θ⋅𝟏.
SumMean(means)	Sum mean function, 𝐟₀ + 𝐟₁ + ….