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Project-declaredLean 4.32.0 · mathlib@81a5d257c8e4

C Lp Norm dft indicator one pow

cLpNorm_dft_indicator_one_pow

Plain-language statement

The 2n2n-th Fourier moment of the indicator of a finite set equals its order-nn additive energy: 1s^2n2n=En(s)\|\widehat{1_s}\|_{2n}^{2n}=E_n(s). This is the standard bridge between Fourier norms and additive tuple counts.

Exact Lean statement

lemma cLpNorm_dft_indicator_one_pow [MeasurableSpace G] [DiscreteMeasurableSpace G] (n : ℕ)
    (s : Finset G) : ‖dft 𝟭_[(s : Set G)]‖ₙ_[↑(2 * n)] ^ (2 * n) = boringEnergy n s

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
lemma cLpNorm_dft_indicator_one_pow [MeasurableSpace G] [DiscreteMeasurableSpace G] (n : )    (s : Finset G) : ‖dft 𝟭_[(s : Set G)]‖ₙ_[↑(2 * n)] ^ (2 * n) = boringEnergy n s := by  obtain rfl | hn := n.eq_zero_or_pos  · simp  refine Complex.ofReal_injective ?_  calc    _ = ⟪dft (𝟭_[(s : Set G)] ∗ᵈ^ n), dft (𝟭_[s] ∗ᵈ^ n)⟫ₙ_[ℂ] := ?_    _ = ⟪𝟭_[(s : Set G), ℂ] ∗ᵈ^ n, 𝟭_[s] ∗ᵈ^ n⟫_[ℂ] := wInner_cWeight_dft _ _    _ = _ := ?_  · rw [cLpNorm_pow_eq_expect_norm (by positivity)]    simp_rw [pow_mul',  norm_pow _ n, Complex.ofReal_expect, Complex.ofReal_pow,       Complex.conj_mul', wInner_cWeight_eq_expect, inner_apply', dft_iterConv_apply]  · simp only [wInner_one_eq_sum, RCLike.inner_apply, boringEnergy_eq, Complex.ofReal_mul,      Complex.ofReal_sum, sq, Complex.ofReal_iterConv,      (((isSelfAdjoint_indicator_one _).iterConv _).apply _).conj_eq,      Complex.ofReal_comp_indicator_one]
Project
Arithmetic Progressions Almost Periodicity
License
Apache-2.0
Commit
afafc42a5326
Source
APAP/Prereqs/Energy.lean:53-68

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Related declarations

Project-declaredLean 4.32.0

Add Dissociated boring Energy le

AddDissociated.boringEnergy_le

Project documentation

If a finite set ss is additively dissociated, then its order-nn additive energy is at most CnnnsnC^n n^n |s|^n, where CC is the project's Chang constant. This is the quantitative dissociated-set estimate used in the proof of Chang's lemma.

additive combinatoricsarithmetic progressionsFourier analysis

Source project: Arithmetic Progressions Almost Periodicity

Person-level attribution pending.

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Project-declaredLean 4.32.0

Linfty almost periodicity

AlmostPeriodicity.linfty_almost_periodicity

Project documentation

An LL^\infty almost-periodicity theorem. Under the small-growth hypothesis σ[A,S]K\sigma[A,S]\le K, and for nonempty finite sets B,CB,C, there is a set of translations TT with TK4096L(C/B)/ε2S|T|\ge K^{-4096\lceil\mathcal L(|C|/|B|)\rceil/\varepsilon^2}|S|. Every tTt\in T changes the normalized convolution μA1BμC\mu_A*1_B*\mu_C by at most ε\varepsilon in LL^\infty.

additive combinatoricsarithmetic progressionsFourier analysis

Source project: Arithmetic Progressions Almost Periodicity

Person-level attribution pending.

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Project-declaredLean 4.32.0

Linfty almost periodicity boosted

AlmostPeriodicity.linfty_almost_periodicity_boosted

Plain-language statement

A boosted LL^\infty almost-periodicity estimate. Under σ[A,S]K\sigma[A,S]\le K, it finds a large set TT, with the stated lower bound TK4096L(C/B)k2/ε2S|T|\ge K^{-4096\lceil\mathcal L(|C|/|B|)\rceil k^2/\varepsilon^2}|S|, such that averaging the target convolution against the kk-fold convolution of μT\mu_T changes it by at most ε\varepsilon in LL^\infty.

additive combinatoricsarithmetic progressionsFourier analysis

Source project: Arithmetic Progressions Almost Periodicity

Person-level attribution pending.

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