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LeanPool.CaffarelliKohnNirenberg.Leray.ForcedRegularisedFourierEnergy

The frequency-wise energy identity of the forced mild equation #

In frequency variables the forced mild equation eq:reg-mild-forced is, at each frequency ξ, the damped Duhamel formula Y(ξ,t) = e^{-λt} B(ξ) + ∫₀ᵗ e^{-λ(t-s)} ℙ(ξ) g(ξ,s) ds with λ = 4π²|ξ|², source g = -2πi ξ·F̂ + Fourier(H), and the Leray symbol ℙ(ξ). This file defines the jointly measurable frequency representative Y and proves, frequency by frequency, the energy identity of the damped formula; the Leray symbol drops out of the source pairing because Y(ξ,s) lies in its range.

The heat decay rate 4π²|ξ|² at a frequency.

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    The heat symbol is the exponential of minus the decay rate times the time.

    The frequency source of the forced mild equation: minus 2πi times the tensor divergence symbol applied to the tensor, plus the force.

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      The frequency representative of the forced mild equation.

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        The divergence part of the frequency source is jointly measurable.

        The frequency integrand of the representative is jointly measurable.

        The pairing of a vector with the divergence part of the source is bounded by half of the weighted squared norms.

        At a frequency where the source is integrable in time, the representative satisfies the damped energy identity with the unprojected source.

        theorem CKN.Leray.forcedFourierRep_energy_identity {B : Foundation.Parabolic.L2Vec3 → ComplexVec3} {Fh : Foundation.Parabolic.L2Vec3 × ℝ → ComplexTensor3} {Hh : Foundation.Parabolic.L2Vec3 × ℝ → ComplexVec3} (hBm : Measurable B) (hB : MeasureTheory.Integrable (fun (ξ : Foundation.Parabolic.L2Vec3) => ‖B ξ‖ ^ 2) MeasureTheory.volume) (hFh : Measurable Fh) (hHh : Measurable Hh) (hBP : ∀ (ξ : Foundation.Parabolic.L2Vec3), (leraySymbol ξ) (B ξ) = B ξ) {t : ℝ} (ht : 0 ≤ t) (hFint : MeasureTheory.Integrable (fun (p : Foundation.Parabolic.L2Vec3 × ℝ) => ‖Fh p‖ ^ 2) (MeasureTheory.volume.prod (MeasureTheory.volume.restrict (Set.Ioc 0 t)))) (hHint : MeasureTheory.Integrable (fun (p : Foundation.Parabolic.L2Vec3 × ℝ) => ‖Hh p‖ ^ 2) (MeasureTheory.volume.prod (MeasureTheory.volume.restrict (Set.Ioc 0 t)))) (hYint : MeasureTheory.Integrable (fun (p : Foundation.Parabolic.L2Vec3 × ℝ) => ‖forcedFourierRep B Fh Hh p‖ ^ 2) (MeasureTheory.volume.prod (MeasureTheory.volume.restrict (Set.Ioc 0 t)))) (hYt : MeasureTheory.Integrable (fun (ξ : Foundation.Parabolic.L2Vec3) => ‖forcedFourierRep B Fh Hh (ξ, t)‖ ^ 2) MeasureTheory.volume) :

        The energy identity of the forced mild equation in frequency variables: integrating the frequency-wise identity gives ∫|Y(t)|² + 2∫λ∫₀ᵗ|Y|² = ∫|B|² + 2∫₀ᵗ∫Re⟨Y, -2πi ξ·F̂⟩ + 2∫₀ᵗ∫Re⟨Y, Fourier(H)⟩, and the weighted dissipation is integrable in frequency and time.