theorem escortPartitionZ_hasDerivAt
(x : Fin J → ℝ) (hx : ∀ j, 0 < x j) (ρ : ℝ) :
HasDerivAt (escortPartitionZ x)
(escortPartitionZ' x ρ) ρ := by
unfold escortPartitionZ escortPartitionZ'
convert HasDerivAt.sum (u := Finset.univ)
(fun j _ => hasDerivAt_rpow_exponent (hx j) ρ)
using 1
ext p; simpThe VRI σ² = T·χ is fundamentally an exponential family identity: