theorem gradient_orthogonal_to_onePerp
(v : Fin J → ℝ) (hv : orthToOne J v) :
∑ j : Fin J, (1 / (↑J : ℝ)) * v j = 0 := by
rw [← Finset.mul_sum]
simp only [orthToOne, vecSum] at hv
rw [hv, mul_zero]CES Estimation Theory: Connecting Theory to Data