Derivative bounds for partial maps along a compact parameter
ProvedNemytskii.iteratedFDeriv_bounds_of_comp_compactfunctional-analysisnonlinear-analysis
Let be proper real normed spaces, a real normed space, of class , and continuous with values in a compact set . Then for : each is , and for every the derivative is jointly continuous and bounded on for every .
Role. Verifies the hypotheses of Nemytskii.exists_contDiff_superposition for integrands that depend on through a compact parameter.
Preamble
import Mathlib open Metric Set Filter Topology BoundedContinuousFunction open scoped ContDiff
Formal statement
namespace Nemytskii
/-- If `Ψ : P × E → F` is `C^∞` (with `P`, `E` proper) and `p : X → P` is continuous with values
in a compact set, then the partial maps `a ↦ Ψ (p x, a)` are `C^∞`, and each of their derivatives
is jointly continuous in `(x, a)` and bounded on `X × closedBall 0 R` for every `R`. -/
theorem iteratedFDeriv_bounds_of_comp_compact {X : Type*} [TopologicalSpace X]
{P E F : Type*} [NormedAddCommGroup P] [NormedSpace ℝ P] [ProperSpace P]
[NormedAddCommGroup E] [NormedSpace ℝ E] [ProperSpace E]
[NormedAddCommGroup F] [NormedSpace ℝ F]
(Ψ : P × E → F) (hΨ : ContDiff ℝ ∞ Ψ) (p : X → P) (hp : Continuous p) (K : Set P)
(hK : IsCompact K) (hpK : ∀ x, p x ∈ K) :
(∀ x, ContDiff ℝ ∞ ((fun x a => Ψ (p x, a)) x)) ∧
(∀ k : ℕ, Continuous (fun y : X × E => iteratedFDeriv ℝ k ((fun x a => Ψ (p 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 (p 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