Bonami–Beckner hypercontractivity on the uniform cube
TheoremVector two-point inequality for nonnegative noise#✓fully proved
StatMech.Probability.vtp_vectorTwoPoint
The vector two-point inequality holds for 0 ≤ ρ ≤ 1.
theorem vtp_vectorTwoPoint {ρ : ℝ} (h0 : 0 ≤ ρ) (h1 : ρ ≤ 1) :
bnt_VectorTwoPoint ρ
def bnt_VectorTwoPoint (ρ : ℝ) : Prop :=
∀ (n : ℕ) (u v : (Fin n → Bool) → ℝ),
(bnt_qnormPow 2 (fun ω => (1 + ρ) / 2 * u ω + (1 - ρ) / 2 * v ω)
+ bnt_qnormPow 2 (fun ω => (1 - ρ) / 2 * u ω + (1 + ρ) / 2 * v ω)) / 2
≤ ((bnt_qnorm 2 u ^ (1 + ρ ^ 2) + bnt_qnorm 2 v ^ (1 + ρ ^ 2)) / 2) ^ (2 / (1 + ρ ^ 2))
MathlibExt/Probability/Hypercontractivity/BonamiTensorize.lean:226
TheoremBonami–Beckner hypercontractive inequality#✓fully proved
StatMech.Probability.vtp_hypercontractivity
The Bonami–Beckner hypercontractive inequality (Bonami 1970; Beckner 1975): for
0 ≤ ρ ≤ 1 and f : (Fin n → Bool) → ℝ, ‖T_ρ f‖₂ ≤ ‖f‖_(1 + ρ²) under the uniform measure.
theorem vtp_hypercontractivity {ρ : ℝ} (h0 : 0 ≤ ρ) (h1 : ρ ≤ 1)
(n : ℕ) (f : (Fin n → Bool) → ℝ) :
bnt_qnorm 2 (bnt_noiseOp ρ f) ≤ bnt_qnorm (1 + ρ ^ 2) f
noncomputable def bnt_qnorm (q : ℝ) (f : (ι → Bool) → ℝ) : ℝ :=
(bnt_qnormPow q f) ^ (1 / q)
MathlibExt/Probability/Hypercontractivity/BonamiTensorize.lean:74
noncomputable def bnt_noiseOp (ρ : ℝ) (f : (ι → Bool) → ℝ) : (ι → Bool) → ℝ :=
fun x => ∑ y : ι → Bool, bnt_noiseKernel ρ x y * f y
MathlibExt/Probability/Hypercontractivity/BonamiTensorize.lean:93
2 fully proved
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