OAI/Combinatorics/ExpectationThreshold/ProbabilitySubsetProduct.lean

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Moments of products on a subset of coordinates

Under the actual product law, observables supported on a finite subset factor into their coordinate expectations. Extending the factors by one outside the subset reduces this to the full product moment identity.

  1. theorem OAI.TalagrandThreshold.FiniteLaw.expectation_pi_subset_product line 22

    Source documentation

    A product on a subset has the product of its actual coordinate means.

    theorem expectation_pi_subset_product (μ : ∀ i, FiniteLaw (A i))
        (S : Finset I) (f : ∀ i, A i → ℝ) :
        (pi μ).expectation (fun ω => ∏ i ∈ S, f i (ω i)) =
          ∏ i ∈ S, (μ i).expectation (f i) := by
    …

    Mentions: OAI.TalagrandThreshold.FiniteLaw, OAI.TalagrandThreshold.FiniteLaw.pi, OAI.TalagrandThreshold.FiniteLaw.expectation

  2. theorem OAI.TalagrandThreshold.FiniteLaw.expectation_pi_subset_product_of_mean line 45

    Source documentation

    Equal coordinate means give the corresponding power of the subset size.

    theorem expectation_pi_subset_product_of_mean (μ : ∀ i, FiniteLaw (A i))
        (S : Finset I) (f : ∀ i, A i → ℝ) (a : ℝ)
        (hmean : ∀ i ∈ S, (μ i).expectation (f i) = a) :
        (pi μ).expectation (fun ω => ∏ i ∈ S, f i (ω i)) = a ^ S.card := by
    …

    Mentions: OAI.TalagrandThreshold.FiniteLaw, OAI.TalagrandThreshold.FiniteLaw.expectation, OAI.TalagrandThreshold.FiniteLaw.pi

  3. theorem OAI.TalagrandThreshold.FiniteLaw.expectation_pi_subset_product_const line 56

    Source documentation

    Identically distributed coordinates give a power of their common mean.

    theorem expectation_pi_subset_product_const {Ω : Type*} [Fintype Ω]
        (μ : FiniteLaw Ω) (S : Finset I) (f : Ω → ℝ) :
        (pi (fun _ : I => μ)).expectation (fun ω => ∏ i ∈ S, f (ω i)) =
          (μ.expectation f) ^ S.card := by
    …

    Mentions: OAI.TalagrandThreshold.FiniteLaw, OAI.TalagrandThreshold.FiniteLaw.pi, OAI.TalagrandThreshold.FiniteLaw.expectation