Derivative bounds are preserved by a bounded linear rescaling of the value
ProvedNemytskii.iteratedFDeriv_bounds_comp_clmfunctional-analysisnonlinear-analysis
Let have partial maps whose derivatives of every order are jointly continuous on and bounded on for every . Let be continuous with . Then has the same properties on .
Role. A closure property of the hypotheses of Nemytskii.exists_contDiff_superposition, used when the unknown enters through an -dependent bounded weight.
Preamble
import Mathlib open Metric Set Filter Topology BoundedContinuousFunction open scoped ContDiff
Formal statement
namespace Nemytskii
/-- Let `Ψ : X → E' → F` have `C^∞` partial maps whose derivatives of every order are jointly
continuous and bounded on `X × closedBall 0 R` for every `R`, and let `L : X → E →L[ℝ] E'` be
continuous and bounded. Then `(x, a) ↦ Ψ x (L x a)` has the same properties. -/
theorem iteratedFDeriv_bounds_comp_clm {X : Type*} [TopologicalSpace X]
{E E' F : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
[NormedAddCommGroup E'] [NormedSpace ℝ E'] [NormedAddCommGroup F] [NormedSpace ℝ F]
(Ψ : X → E' → F) (hs : ∀ x, ContDiff ℝ ∞ (Ψ x))
(hc : ∀ k : ℕ, Continuous (fun p : X × E' => iteratedFDeriv ℝ k (Ψ p.1) p.2))
(hb : ∀ (k : ℕ) (R : ℝ), ∃ C : ℝ, ∀ x, ∀ a ∈ closedBall (0 : E') R,
‖iteratedFDeriv ℝ k (Ψ x) a‖ ≤ C)
(L : X → E →L[ℝ] E') (hL : Continuous L) (Λ : ℝ) (hΛ : ∀ x, ‖L x‖ ≤ Λ) :
(∀ x, ContDiff ℝ ∞ ((fun x a => Ψ x (L x a)) x)) ∧
(∀ k : ℕ, Continuous (fun y : X × E => iteratedFDeriv ℝ k ((fun x a => Ψ x (L x a)) y.1) y.2)) ∧
∀ (k : ℕ) (R : ℝ), ∃ C : ℝ, ∀ x, ∀ a ∈ closedBall (0 : E) R,
‖iteratedFDeriv ℝ k ((fun x a => Ψ x (L x a)) x) a‖ ≤ C := by
sorry
end Nemytskii
Source
Superposition (Nemytskii) operators, cf. J. Appell and P. P. Zabrejko, Nonlinear Superposition Operators, Cambridge Univ. Press 1990; used toward U. Hryniewicz, Fast finite-energy planes in symplectizations and applications, Trans. AMS 364 (2012), arXiv:0812.4076, Lemmas 6.10 and 6.20