Integral tendsto of Lploc tendsto
integral_tendsto_of_Lploc_tendsto
Plain-language statement
If f i converges to g in Lᵖ(U), then for any test function ψ ∈ C_c^∞(U), the integrals ∫ f i * ψ ∂μU converge to ∫ g * ψ ∂μU.
Exact Lean statement
lemma integral_tendsto_of_Lploc_tendsto
{U : Set (Fin d → ℝ)}
{p : ℝ≥0∞}
{ψ : (Fin d → ℝ) → ℝ}
{f : ℕ → (Fin d → ℝ) → ℝ}
{g : (Fin d → ℝ) → ℝ}
(hp : 1 ≤ p)
(hf : ∀ i, MemLp (f i) p (μU d U))
(hg : MemLp g p (μU d U))
(hψ : ψ ∈ Cc_inftyU d U)
(hconv : Tendsto (fun i => eLpNorm (fun x => f i x - g x) p (μU d U))
atTop (𝓝 0))
: Tendsto (fun i => ∫ x, f i x * ψ x ∂μU d U) atTop (𝓝 (∫ x, g x * ψ x ∂μU d U))Formal artifact
Lean source
lemma integral_tendsto_of_Lploc_tendsto {U : Set (Fin d → ℝ)} {p : ℝ≥0∞} {ψ : (Fin d → ℝ) → ℝ} {f : ℕ → (Fin d → ℝ) → ℝ} {g : (Fin d → ℝ) → ℝ} (hp : 1 ≤ p) (hf : ∀ i, MemLp (f i) p (μU d U)) (hg : MemLp g p (μU d U)) (hψ : ψ ∈ Cc_inftyU d U) (hconv : Tendsto (fun i => eLpNorm (fun x => f i x - g x) p (μU d U)) atTop (𝓝 0)) : Tendsto (fun i => ∫ x, f i x * ψ x ∂μU d U) atTop (𝓝 (∫ x, g x * ψ x ∂μU d U)) := by let q : ℝ≥0∞ := ENNReal.conjExponent p haveI : Fact (1 ≤ p) := ⟨hp⟩ have hpq : p.HolderConjugate q := inferInstance letI : p.HolderTriple q 1 := hpq have hψ_Lq : MemLp ψ q (μU d U) := by haveI : IsFiniteMeasureOnCompacts (μU d U) := by unfold μU; infer_instance exact (hψ.2.2.continuous).memLp_of_hasCompactSupport hψ.1 have hInt_g : Integrable (fun x => g x * ψ x) (μU d U) := by simpa [Pi.mul_apply] using MemLp.integrable_mul hg hψ_Lq have hfg : ∀ i, MemLp (fun x => f i x - g x) p (μU d U) := fun i => (hf i).sub hg have hInt_diff : ∀ i, Integrable (fun x => (f i x - g x) * ψ x) (μU d U) := by intro i simpa [Pi.mul_apply] using MemLp.integrable_mul (hfg i) hψ_Lq have hstep2 : Tendsto (fun i => ∫ x, (f i x - g x) * ψ x ∂μU d U) atTop (𝓝 0) := by set C := eLpNorm ψ q (μU d U) have hC_fin : C ≠ ⊤ := hψ_Lq.eLpNorm_lt_top.ne have hHolder : ∀ i, ‖∫ x, (f i x - g x) * ψ x ∂μU d U‖ ≤ (eLpNorm (fun x => f i x - g x) p (μU d U) * C).toReal := fun i => by have h1 : ‖∫ x, (f i x - g x) * ψ x ∂μU d U‖ ≤ ∫ x, ‖f i x - g x‖ * ‖ψ x‖ ∂μU d U := (norm_integral_le_integral_norm _).trans (le_of_eq (by congr 1; ext x; exact norm_mul _ _)) have h2 : ∫ x, ‖f i x - g x‖ * ‖ψ x‖ ∂μU d U ≤ (eLpNorm (fun x => f i x - g x) p (μU d U) * C).toReal := by simp_rw [← norm_mul] have h_int := hInt_diff i calc ∫ x, ‖(f i x - g x) * ψ x‖ ∂μU d U = (eLpNorm (fun x => (f i x - g x) * ψ x) 1 (μU d U)).toReal := by rw [eLpNorm_one_eq_lintegral_enorm] exact (integral_norm_eq_lintegral_enorm h_int.aestronglyMeasurable) _ ≤ (eLpNorm (fun x => f i x - g x) p (μU d U) * C).toReal := by have hR_ne_top : eLpNorm (fun x => f i x - g x) p (μU d U) * C ≠ ⊤ := by exact ENNReal.mul_ne_top (hfg i).eLpNorm_lt_top.ne hC_fin exact (ENNReal.toReal_le_toReal (memLp_one_iff_integrable.mpr h_int).eLpNorm_lt_top.ne hR_ne_top).mpr (by simpa [C, smul_eq_mul, mul_comm, mul_left_comm, mul_assoc] using (MeasureTheory.eLpNorm_smul_le_mul_eLpNorm (μ := μU d U) (p := p) (q := q) (r := 1) (f := ψ) hψ_Lq.aestronglyMeasurable (hfg i).aestronglyMeasurable)) exact h1.trans h2 exact squeeze_zero_norm hHolder (by simp_rw [ENNReal.toReal_mul] simpa using ((ENNReal.tendsto_toReal zero_ne_top).comp hconv).mul_const C.toReal) have heq : ∀ i, ∫ x, f i x * ψ x ∂μU d U = ∫ x, (f i x - g x) * ψ x ∂μU d U + ∫ x, g x * ψ x ∂μU d U := fun i => by rw [← integral_add (hInt_diff i) hInt_g] congr 1; ext x; ring simp_rw [heq] simpa using hstep2.add tendsto_const_nhds- Project
- PDE
- License
- Apache-2.0
- Commit
- 0ab5d79a0d7a
- Source
- PDE/SobolevSpace/SobolevSpaces.lean:564-642
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