Bound on an intermediate derivative of a smooth map on a half-plane by its neighbouring derivatives
ProvedFiniteEnergyPlane.norm_iteratedFDeriv_succ_le_of_halfPlaneasymptotic-analysisinequalitiesreal-analysis
Let be a real normed space, , and let be on the open half-plane . Let , let with , and let , . Suppose that for every with we have and . Then
This is a pointwise interpolation inequality for consecutive derivative orders on a half-plane, using only the region to the right of the point. It is meant for estimating derivatives of maps defined on cylindrical ends.
Formalization Note is iteratedFDeriv ℝ k f, with the norm of continuous multilinear maps on ℝ × ℝ (sup norm). The half-plane is Set.Ioi s₀ ×ˢ Set.univ, and the bounds are assumed on {q | p.1 ≤ q.1}.
Preamble
import Mathlib
Formal statement
namespace FiniteEnergyPlane
open scoped ContDiff
/-- On a half-plane `{s > s₀}`, the norm of the `(j+1)`-st derivative of a smooth map at `p` is
bounded by `2 (2A/h + Bh)` for every `h > 0`, where `A` and `B` bound the `j`-th and `(j+2)`-nd
derivatives on `{s ≥ p.1}`. -/
theorem norm_iteratedFDeriv_succ_le_of_halfPlane {F : Type*} [NormedAddCommGroup F]
[NormedSpace ℝ F] (f : ℝ × ℝ → F) (s₀ : ℝ)
(hf : ContDiffOn ℝ ∞ f (Set.Ioi s₀ ×ˢ Set.univ)) (j : ℕ) (p : ℝ × ℝ) (hp : s₀ < p.1)
(A B h : ℝ) (hh : 0 < h)
(hA : ∀ q : ℝ × ℝ, p.1 ≤ q.1 → ‖iteratedFDeriv ℝ j f q‖ ≤ A)
(hB : ∀ q : ℝ × ℝ, p.1 ≤ q.1 → ‖iteratedFDeriv ℝ (j + 2) f q‖ ≤ B) :
‖iteratedFDeriv ℝ (j + 1) f p‖ ≤ 2 * (2 * A / h + B * h) := by
sorry
end FiniteEnergyPlane
Source
Elementary real analysis (Landau-Kolmogorov type inequality); used for U. Hryniewicz, J. Symplectic Geom. 12 (2014), Theorem 2.10