theorem escort_variance_nonneg [NeZero J]
(x : Fin J → ℝ) (hx : ∀ j, 0 < x j) (ρ : ℝ)
(f : Fin J → ℝ) :
0 ≤ escortVariance x ρ f := by
unfold escortVariance escortExpectation
rw [variance_identity _ _ (escort_prob_sum_one x hx ρ)]
apply Finset.sum_nonneg
intro j _
apply mul_nonneg
· exact div_nonneg (le_of_lt (rpow_pos_of_pos (hx j) ρ))
(le_of_lt (escortPartitionZ_pos x hx ρ))
· exact sq_nonneg _CES Estimation Theory: Connecting Theory to Data