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LeanPool.CaffarelliKohnNirenberg.Leray.CompactnessGradientProjection

Compactness Gradient Projection #

Supporting estimates for the Navier–Stokes development.

theorem CKN.Leray.weak_l2_compLpL {α : Type u_1} {E : Type u_2} {F : Type u_3} [MeasurableSpace α] [NormedAddCommGroup E] [InnerProductSpace ℝ E] [CompleteSpace E] [NormedAddCommGroup F] [InnerProductSpace ℝ F] [CompleteSpace F] {μ : MeasureTheory.Measure α} (L : E →L[ℝ] F) (f : ℕ → ↥(MeasureTheory.Lp E 2 μ)) (g : ↥(MeasureTheory.Lp E 2 μ)) (hweak : ∀ (w : ↥(MeasureTheory.Lp E 2 μ)), Filter.Tendsto (fun (k : ℕ) => inner ℝ (f k) w) Filter.atTop (nhds (inner ℝ g w))) (w : ↥(MeasureTheory.Lp F 2 μ)) :
Filter.Tendsto (fun (k : ℕ) => inner ℝ (L.compLp (f k)) w) Filter.atTop (nhds (inner ℝ (L.compLp g) w))

Weak convergence in Hilbert-valued L² is preserved by a continuous linear map of the fibers.

theorem CKN.Leray.weak_l2_scalar_integral_of_fiber_weak {α : Type u_1} {E : Type u_2} [MeasurableSpace α] [NormedAddCommGroup E] [InnerProductSpace ℝ E] [CompleteSpace E] {μ : MeasureTheory.Measure α} (L : E →L[ℝ] ℝ) (F : ℕ → α → E) (G : ↥(MeasureTheory.Lp E 2 μ)) (hF : ∀ (k : ℕ), MeasureTheory.MemLp (F k) 2 μ) (hweak : ∀ (v : ↥(MeasureTheory.Lp E 2 μ)), Filter.Tendsto (fun (k : ℕ) => inner ℝ (MeasureTheory.MemLp.toLp (F k) ⋯) v) Filter.atTop (nhds (inner ℝ G v))) (w : α → ℝ) (hw : MeasureTheory.MemLp w 2 μ) :
Filter.Tendsto (fun (k : ℕ) => ∫ (x : α), L (F k x) * w x ∂μ) Filter.atTop (nhds (∫ (x : α), L (↑↑G x) * w x ∂μ))

Applying a scalar functional to a weakly convergent L² sequence gives convergence of its integrals against every scalar L² test.

Evaluation of one matrix entry is continuous on the Euclidean gradient fiber.

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