Documentation

Mathlib.Probability.Kernel.CondCdf

Conditional cumulative distribution function #

Given ρ : measure (α × ℝ), we define the conditional cumulative distribution function (conditional cdf) of ρ. It is a function cond_cdf ρ : α → ℝ → ℝ such that if ρ is a finite measure, then for all a : α cond_cdf ρ a is monotone and right-continuous with limit 0 at -∞ and limit 1 at +∞, and such that for all x : ℝ, a ↦ cond_cdf ρ a x is measurable. For all x : ℝ and measurable set s, that function satisfies ∫⁻ a in s, ennreal.of_real (cond_cdf ρ a x) ∂ρ.fst = ρ (s ×ˢ Iic x).

Main definitions #

Main statements #

References #

The construction of the conditional cdf in this file follows the proof of Theorem 3.4 in [O. Kallenberg, Foundations of modern probability][kallenberg2021].

TODO #

theorem Directed.sequence_anti {α : Type u_1} {β : Type u_2} [Encodable α] [Inhabited α] [Preorder β] {f : αβ} (hf : Directed (fun x x_1 => x x_1) f) :
theorem Directed.sequence_le {α : Type u_1} {β : Type u_2} [Encodable α] [Inhabited α] [Preorder β] {f : αβ} (hf : Directed (fun x x_1 => x x_1) f) (a : α) :
theorem prod_iInter {α : Type u_1} {β : Type u_2} {ι : Type u_3} {s : Set α} {t : ιSet β} [hι : Nonempty ι] :
s ×ˢ ⋂ (i : ι), t i = ⋂ (i : ι), s ×ˢ t i
theorem Real.iUnion_Iic_rat :
⋃ (r : ), Set.Iic r = Set.univ
theorem Real.iInter_Iic_rat :
⋂ (r : ), Set.Iic r =
theorem atBot_le_nhds_bot {α : Type u_4} [TopologicalSpace α] [LinearOrder α] [OrderBot α] [OrderTopology α] :
Filter.atBot nhds
theorem atTop_le_nhds_top {α : Type u_4} [TopologicalSpace α] [LinearOrder α] [OrderTop α] [OrderTopology α] :
Filter.atTop nhds
theorem tendsto_of_antitone {ι : Type u_4} {α : Type u_5} [Preorder ι] [TopologicalSpace α] [ConditionallyCompleteLinearOrder α] [OrderTopology α] {f : ια} (h_mono : Antitone f) :
Filter.Tendsto f Filter.atTop Filter.atBot l, Filter.Tendsto f Filter.atTop (nhds l)
theorem ENNReal.ofReal_cinfi {α : Type u_1} (f : α) [Nonempty α] :
ENNReal.ofReal (⨅ (i : α), f i) = ⨅ (i : α), ENNReal.ofReal (f i)
theorem lintegral_iInf_directed_of_measurable {α : Type u_1} {β : Type u_2} {mα : MeasurableSpace α} [Countable β] {f : βαENNReal} {μ : MeasureTheory.Measure α} (hμ : μ 0) (hf : ∀ (b : β), Measurable (f b)) (hf_int : ∀ (b : β), ∫⁻ (a : α), f b aμ ) (h_directed : Directed (fun x x_1 => x x_1) f) :
∫⁻ (a : α), ⨅ (b : β), f b aμ = ⨅ (b : β), ∫⁻ (a : α), f b aμ

Monotone convergence for an infimum over a directed family and indexed by a countable type

noncomputable def MeasureTheory.Measure.IicSnd {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (r : ) :

Measure on α such that for a measurable set s, ρ.Iic_snd r s = ρ (s ×ˢ Iic r).

Instances For
    theorem MeasureTheory.Measure.IicSnd_apply {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (r : ) {s : Set α} (hs : MeasurableSet s) :
    ↑(MeasureTheory.Measure.IicSnd ρ r) s = ρ (s ×ˢ Set.Iic r)
    theorem MeasureTheory.Measure.IicSnd_univ {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (r : ) :
    ↑(MeasureTheory.Measure.IicSnd ρ r) Set.univ = ρ (Set.univ ×ˢ Set.Iic r)
    theorem MeasureTheory.Measure.iInf_IicSnd_gt {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (t : ) {s : Set α} (hs : MeasurableSet s) [MeasureTheory.IsFiniteMeasure ρ] :
    ⨅ (r : { r' // t < r' }), ↑(MeasureTheory.Measure.IicSnd ρ r) s = ↑(MeasureTheory.Measure.IicSnd ρ t) s
    theorem MeasureTheory.Measure.tendsto_IicSnd_atTop {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) {s : Set α} (hs : MeasurableSet s) :
    Filter.Tendsto (fun r => ↑(MeasureTheory.Measure.IicSnd ρ r) s) Filter.atTop (nhds (↑(MeasureTheory.Measure.fst ρ) s))
    theorem MeasureTheory.Measure.tendsto_IicSnd_atBot {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] {s : Set α} (hs : MeasurableSet s) :
    Filter.Tendsto (fun r => ↑(MeasureTheory.Measure.IicSnd ρ r) s) Filter.atBot (nhds 0)

    Auxiliary definitions #

    We build towards the definition of probability_theory.cond_cdf. We first define probability_theory.pre_cdf, a function defined on α × ℚ with the properties of a cdf almost everywhere. We then introduce probability_theory.cond_cdf_rat, a function on α × ℚ which has the properties of a cdf for all a : α. We finally extend to .

    noncomputable def ProbabilityTheory.preCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (r : ) :
    αENNReal

    pre_cdf is the Radon-Nikodym derivative of ρ.IicSnd with respect to ρ.fst at each r : ℚ. This function ℚ → α → ℝ≥0∞ is such that for almost all a : α, the function ℚ → ℝ≥0∞ satisfies the properties of a cdf (monotone with limit 0 at -∞ and 1 at +∞, right-continuous).

    We define this function on and not because is countable, which allows us to prove properties of the form ∀ᵐ a ∂ρ.fst, ∀ q, P (pre_cdf q a), instead of the weaker ∀ q, ∀ᵐ a ∂ρ.fst, P (pre_cdf q a).

    Instances For
      theorem ProbabilityTheory.set_lintegral_iInf_gt_preCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] (t : ) {s : Set α} (hs : MeasurableSet s) :
      ∫⁻ (x : α) in s, ⨅ (r : ↑(Set.Ioi t)), ProbabilityTheory.preCdf ρ (r) xMeasureTheory.Measure.fst ρ = ↑(MeasureTheory.Measure.IicSnd ρ t) s
      theorem ProbabilityTheory.tendsto_lintegral_preCdf_atTop {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] :
      Filter.Tendsto (fun r => ∫⁻ (a : α), ProbabilityTheory.preCdf ρ r aMeasureTheory.Measure.fst ρ) Filter.atTop (nhds (ρ Set.univ))
      theorem ProbabilityTheory.inf_gt_preCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] :
      ∀ᵐ (a : α) ∂MeasureTheory.Measure.fst ρ, ∀ (t : ), ⨅ (r : ↑(Set.Ioi t)), ProbabilityTheory.preCdf ρ (r) a = ProbabilityTheory.preCdf ρ t a
      structure ProbabilityTheory.HasCondCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) :

      A product measure on α × ℝ is said to have a conditional cdf at a : α if preCdf is monotone with limit 0 at -∞ and 1 at +∞, and is right continuous. This property holds almost everywhere (see has_cond_cdf_ae).

      Instances For

        A measurable set of elements of α such that ρ has a conditional cdf at all a ∈ condCdfSet.

        Instances For
          noncomputable def ProbabilityTheory.condCdfRat {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) :
          α

          Conditional cdf of the measure given the value on α, restricted to the rationals. It is defined to be pre_cdf if a ∈ condCdfSet, and a default cdf-like function otherwise. This is an auxiliary definition used to define cond_cdf.

          Instances For
            theorem ProbabilityTheory.condCdfRat_of_not_mem {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) (h : ¬a ProbabilityTheory.condCdfSet ρ) {r : } :
            ProbabilityTheory.condCdfRat ρ a r = if r < 0 then 0 else 1
            theorem ProbabilityTheory.inf_gt_condCdfRat {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) (t : ) :
            @[irreducible]
            noncomputable def ProbabilityTheory.condCdf' {α : Type u_4} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) :
            α

            Conditional cdf of the measure given the value on α, as a plain function. This is an auxiliary definition used to define cond_cdf.

            Instances For
              theorem ProbabilityTheory.condCdf'_def {α : Type u_4} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) (t : ) :
              ProbabilityTheory.condCdf' ρ a t = ⨅ (r : { r' // t < r' }), ProbabilityTheory.condCdfRat ρ a r
              theorem ProbabilityTheory.condCdf'_def' {α : Type u_1} {mα : MeasurableSpace α} {ρ : MeasureTheory.Measure (α × )} {a : α} {x : } :
              ProbabilityTheory.condCdf' ρ a x = ⨅ (r : { r // x < r }), ProbabilityTheory.condCdfRat ρ a r

              Conditional cdf #

              noncomputable def ProbabilityTheory.condCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) :

              Conditional cdf of the measure given the value on α, as a Stieltjes function.

              Instances For
                theorem ProbabilityTheory.condCdf_nonneg {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) (r : ) :

                The conditional cdf is non-negative for all a : α.

                theorem ProbabilityTheory.condCdf_le_one {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) (x : ) :

                The conditional cdf is lower or equal to 1 for all a : α.

                theorem ProbabilityTheory.tendsto_condCdf_atBot {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) :
                Filter.Tendsto (↑(ProbabilityTheory.condCdf ρ a)) Filter.atBot (nhds 0)

                The conditional cdf tends to 0 at -∞ for all a : α.

                theorem ProbabilityTheory.tendsto_condCdf_atTop {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) (a : α) :
                Filter.Tendsto (↑(ProbabilityTheory.condCdf ρ a)) Filter.atTop (nhds 1)

                The conditional cdf tends to 1 at +∞ for all a : α.

                The conditional cdf is a measurable function of a : α for all x : ℝ.

                theorem ProbabilityTheory.set_lintegral_condCdf_rat {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] (r : ) {s : Set α} (hs : MeasurableSet s) :
                ∫⁻ (a : α) in s, ENNReal.ofReal (↑(ProbabilityTheory.condCdf ρ a) r)MeasureTheory.Measure.fst ρ = ρ (s ×ˢ Set.Iic r)

                Auxiliary lemma for set_lintegral_cond_cdf.

                theorem ProbabilityTheory.set_lintegral_condCdf {α : Type u_1} {mα : MeasurableSpace α} (ρ : MeasureTheory.Measure (α × )) [MeasureTheory.IsFiniteMeasure ρ] (x : ) {s : Set α} (hs : MeasurableSet s) :
                ∫⁻ (a : α) in s, ENNReal.ofReal (↑(ProbabilityTheory.condCdf ρ a) x)MeasureTheory.Measure.fst ρ = ρ (s ×ˢ Set.Iic x)

                The conditional cdf is a strongly measurable function of a : α for all x : ℝ.

                The function a ↦ (condCdf ρ a).measure is measurable.