Measurability of Bernstein numbers and of pushforwards
Lax606786.MeasurableOperatorFamilies · concepts/Lax606786/MeasurableOperatorFamilies.lean · lax-606786
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Theorem
Let be a separable real normed space with a -algebra containing the open sets, and let be a strongly measurable family of bounded operators on (each measurable). Then for :
- is measurable, and so is ;
- is measurable for every measurable (if the -algebra of is Borel);
- is measurable for every subspace , and is measurable for every measurable (if the -algebra of is Borel);
- if moreover is complete and is measurable, then any with for every is measurable.
For the norm topology on the operators, is itself Borel measurable.
Concept map
Evidence
This concept declares 7 statements. Each proof establishes one of them relative to its assumptions.
1 measurable_apply proven
2 measurable_bernsteinNumber proven
3 measurable_bernsteinNumber_norm proven
4 measurable_growth proven
5 measurable_growth_moving proven
6 measurable_opNorm proven
7 measurable_pushforward proven
In the paper
- page 3 of this submission's paper
Lean source view on GitLab
| 1 | import Lax606786.OperatorStatistics |
| 2 | import Mathlib.MeasureTheory.Constructions.BorelSpace.Basic |
| 3 | |
| 4 | import Mathlib.MeasureTheory.Constructions.BorelSpace.ContinuousLinearMap |
| 5 | /-! |
| 6 | --- |
| 7 | title: Measurability of Bernstein numbers and of pushforwards |
| 8 | type: theorem |
| 9 | --- |
| 10 | Let be a separable real normed space with a -algebra containing the open sets, and let |
| 11 | be a strongly measurable family of bounded operators on (each |
| 12 | measurable). Then for : |
| 13 | |
| 14 | - is measurable, and so is ; |
| 15 | - is measurable for every measurable (if the |
| 16 | -algebra of is Borel); |
| 17 | - is measurable for every subspace , and |
| 18 | is measurable for every measurable |
| 19 | (if the -algebra of is Borel); |
| 20 | - if moreover is complete and is measurable, then any |
| 21 | with for every is |
| 22 | measurable. |
| 23 | |
| 24 | For the norm topology on the operators, is itself Borel measurable. |
| 25 | -/ |
| 26 | |
| 27 | namespace Lax606786.MeasurableOperatorFamilies |
| 28 | |
| 29 | open TopologicalSpace |
| 30 | open Lax606786.BanachGrassmannian Lax606786.OperatorStatistics |
| 31 | |
| 32 | /-- `ω ↦ ‖T_ω‖` is measurable for a strongly measurable family `T` on a separable space. -/ |
| 33 | axiom measurable_opNorm {Ω X Y : Type*} [MeasurableSpace Ω] [NormedAddCommGroup X] |
| 34 | [NormedSpace ℝ X] [NormedAddCommGroup Y] [NormedSpace ℝ Y] [MeasurableSpace Y] [BorelSpace Y] |
| 35 | [SeparableSpace X] {T : Ω → X →L[ℝ] Y} (hT : ∀ x, Measurable fun ω => T ω x) : |
| 36 | Measurable fun ω => ‖T ω‖ |
| 37 | |
| 38 | variable {X : Type*} [NormedAddCommGroup X] [NormedSpace ℝ X] |
| 39 | |
| 40 | /-- `ω ↦ ρ_k(A_ω)` is measurable for strongly measurable `A`. -/ |
| 41 | axiom measurable_bernsteinNumber {Ω : Type*} [MeasurableSpace Ω] [MeasurableSpace X] |
| 42 | [OpensMeasurableSpace X] [SeparableSpace X] (k : ℕ) [NeZero k] {A : Ω → X →L[ℝ] X} |
| 43 | (hA : ∀ x : X, Measurable fun ω => A ω x) : |
| 44 | Measurable fun ω => bernsteinNumber (A ω) k |
| 45 | |
| 46 | /-- A strongly measurable family applied to a measurable vector field is measurable. -/ |
| 47 | axiom measurable_apply {Ω : Type*} [MeasurableSpace Ω] [MeasurableSpace X] |
| 48 | [BorelSpace X] [SeparableSpace X] {A : Ω → X →L[ℝ] X} |
| 49 | (hA : ∀ x : X, Measurable fun ω => A ω x) {v : Ω → X} (hv : Measurable v) : |
| 50 | Measurable fun ω => A ω (v ω) |
| 51 | |
| 52 | /-- `ω ↦ g(A_ω, V)` is measurable for a fixed subspace `V ≠ 0`. -/ |
| 53 | axiom measurable_growth {Ω : Type*} [MeasurableSpace Ω] [MeasurableSpace X] |
| 54 | [OpensMeasurableSpace X] [SeparableSpace X] {A : Ω → X →L[ℝ] X} |
| 55 | (hA : ∀ x : X, Measurable fun ω => A ω x) (V : Submodule ℝ X) |
| 56 | (hV : (Metric.sphere (0 : X) 1 ∩ (V : Set X)).Nonempty) : |
| 57 | Measurable fun ω => growth (A ω) V |
| 58 | |
| 59 | /-- `ω ↦ g(A_ω, E(ω))` is measurable for a measurable family `E` in `𝒢_k X`. -/ |
| 60 | axiom measurable_growth_moving {Ω : Type*} [MeasurableSpace Ω] [MeasurableSpace X] |
| 61 | [BorelSpace X] [SeparableSpace X] {m : ℕ} [NeZero m] |
| 62 | {A : Ω → X →L[ℝ] X} (hA : ∀ x : X, Measurable fun ω => A ω x) |
| 63 | {E : Ω → GrassmannianFin X m} (hE : Measurable E) : |
| 64 | Measurable fun ω => growth (A ω) ((E ω).1 : Submodule ℝ X) |
| 65 | |
| 66 | /-- `ω ↦ A_ω E(ω)` is measurable in `𝒢_k X`. -/ |
| 67 | axiom measurable_pushforward {Ω : Type*} [MeasurableSpace Ω] [MeasurableSpace X] |
| 68 | [OpensMeasurableSpace X] [SeparableSpace X] [CompleteSpace X] (k : ℕ) |
| 69 | [NeZero k] (E : Ω → GrassmannianFin X k) (hE : Measurable E) |
| 70 | (A : Ω → X →L[ℝ] X) (hA : ∀ x : X, Measurable fun ω => A ω x) |
| 71 | (F : Ω → GrassmannianFin X k) |
| 72 | (hF : ∀ ω, (F ω).1 = Submodule.map ((A ω : X →ₗ[ℝ] X)) (E ω).1) : |
| 73 | Measurable F |
| 74 | |
| 75 | /-- For the norm topology on the operators, `T ↦ ρ_k(T)` is measurable. -/ |
| 76 | axiom measurable_bernsteinNumber_norm [SeparableSpace X] (k : ℕ) [NeZero k] |
| 77 | [Nonempty (GrassmannianFin X k)] : |
| 78 | Measurable (fun T : X →L[ℝ] X => bernsteinNumber T k) |
| 79 | |
| 80 | end Lax606786.MeasurableOperatorFamilies |
| 81 |
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