Locally integrable, class D, class DL #
The condition that the running supremum process (t, ω) ↦ sup_{s ≤ t} ‖X s ω‖ is strongly
measurable as a function on the product.
Equations
- ProbabilityTheory.HasStronglyMeasurableSupProcess X = MeasureTheory.StronglyMeasurable fun (tω : ι × Ω) => ⨆ (s : ι), ⨆ (_ : s ≤ tω.1), ‖X s tω.2‖ₑ
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A stochastic process has integrable supremum if the function (t, ω) ↦ sup_{s ≤ t} ‖X s ω‖
is strongly measurable and if for all t, the random variable ω ↦ sup_{s ≤ t} ‖X s ω‖
is integrable.
Equations
- ProbabilityTheory.HasIntegrableSup X P = (ProbabilityTheory.HasStronglyMeasurableSupProcess X ∧ ∀ (t : ι), MeasureTheory.Integrable (fun (ω : Ω) => ⨆ (s : ι), ⨆ (_ : s ≤ t), ‖X s ω‖ₑ) P)
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A stochastic process has locally integrable supremum if it satisfies locally the property that
for all t, the random variable ω ↦ sup_{s ≤ t} ‖X s ω‖ is integrable.
Equations
- ProbabilityTheory.HasLocallyIntegrableSup X 𝓕 P = ProbabilityTheory.Locally (fun (x : ι → Ω → E) => ProbabilityTheory.HasIntegrableSup x P) 𝓕 X P
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A stochastic process $(X_t)$ is of class D (or in the Doob-Meyer class) if it is adapted and the set $\{X_\tau \mid \tau \text{ is a finite stopping time}\}$ is uniformly integrable.
- progMeasurable : MeasureTheory.ProgMeasurable 𝓕 X
- uniformIntegrable : MeasureTheory.UniformIntegrable (fun (τ : ↑{T : Ω → WithTop ι | MeasureTheory.IsStoppingTime 𝓕 T ∧ ∀ (ω : Ω), T ω ≠ ⊤}) => MeasureTheory.stoppedValue X ↑τ) 1 P
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A stochastic process $(X_t)$ is of class DL if it is adapted and for all $t$, the set $\{X_\tau \mid \tau \text{ is a stopping time with } \tau \le t\}$ is uniformly integrable.
- progMeasurable : MeasureTheory.ProgMeasurable 𝓕 X
- uniformIntegrable (t : ι) : MeasureTheory.UniformIntegrable (fun (τ : ↑{T : Ω → WithTop ι | MeasureTheory.IsStoppingTime 𝓕 T ∧ ∀ (ω : Ω), T ω ≤ ↑t}) => MeasureTheory.stoppedValue X ↑τ) 1 P
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If {stoppedValue X T : T is a bounded stopping time} is uniformly integrable, then X is
of class D.