Local properties of processes #
A localizing sequence is a sequence of stopping times that tends almost surely to infinity.
- isStoppingTime (n : ℕ) : MeasureTheory.IsStoppingTime 𝓕 (τ n)
- tendsto_top : ∀ᵐ (ω : Ω) ∂P, Filter.Tendsto (fun (x : ℕ) => τ x ω) Filter.atTop (nhds ⊤)
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A localizing sequence is a sequence of stopping times that is almost surely increasing and tends almost surely to infinity.
- tendsto_top : ∀ᵐ (ω : Ω) ∂P, Filter.Tendsto (fun (x : ℕ) => τ x ω) Filter.atTop (nhds ⊤)
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A stochastic process X is said to satisfy a property p locally with respect to a
filtration 𝓕 if there exists a localizing sequence (τ_n) such that for all n, the stopped
process of fun i ↦ {ω | ⊥ < τ n ω}.indicator (X i) satisfies p.
Equations
- One or more equations did not get rendered due to their size.
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A localizing sequence, witness of the local property of the stochastic process.
Equations
- hX.localSeq = Exists.choose hX
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A property of stochastic processes is said to be stable if it is preserved under taking the stopped process by a stopping time.
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- One or more equations did not get rendered due to their size.
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A stable property holds locally p for X if there exists a pre-localizing sequence τ for
which the stopped process of fun i ↦ {ω | ⊥ < τ n ω}.indicator (X i) satisfies p.
Auxliary defintion for isPreLocalizingSequence_of_isLocalizingSequence which constructs a
strictly increasing sequence from a given sequence.
Equations
- ProbabilityTheory.mkStrictMonoAux x 0 = x 0
- ProbabilityTheory.mkStrictMonoAux x n.succ = max (x (n + 1)) (ProbabilityTheory.mkStrictMonoAux x n) + 1
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A stable property holding locally is idempotent.
If p implies q locally, then p locally implies q locally.
Given a property on paths which holds almost surely for a stochastic process, we construct a localizing sequence by setting the stopping time to be ∞ whenever the property holds.
Equations
- ProbabilityTheory.LocalizingSequence_of_prop X p = Function.const ℕ fun (ω : Ω) => if p fun (x : ι) => X x ω then ⊤ else ⊥