The levels of an Oseledets decomposition
Lax606786.OseledetsLevels · concepts/Lax606786/OseledetsLevels.lean · lax-606786
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Definition
Let be a cocycle on a Banach space and its distinct exponents. For , the decomposition after the first fast spaces (level ) consists of measurable families of
- the newest fast space , of dimension ;
- the sum of all fast spaces so far, of dimension ;
- a slow space and a projection onto along ,
such that, almost surely: is real, , and first occurs at index among the (so ); is equivariant, has dimension and grows at rate in norm and in slowest growth; , and grows at rate at least ; is strongly measurable, tempered, idempotent with range and kernel , and commutes with the cocycle; and grows at rate , with .
These are the stages of the induction by which the decomposition is built in the proof of Theorem 3 of Lee (2024).
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| 1 | import Lax606786.Cocycles |
| 2 | import Lax606786.BanachGrassmannian |
| 3 | |
| 4 | /-! |
| 5 | --- |
| 6 | title: The levels of an Oseledets decomposition |
| 7 | type: definition |
| 8 | --- |
| 9 | Let be a cocycle on a Banach space and its |
| 10 | distinct exponents. For , the *decomposition after the first fast spaces* (level ) |
| 11 | consists of measurable families of |
| 12 | |
| 13 | - the newest fast space , of dimension ; |
| 14 | - the sum of all fast spaces so far, |
| 15 | of dimension ; |
| 16 | - a slow space and a projection onto along |
| 17 | , |
| 18 | |
| 19 | such that, almost surely: is real, , and |
| 20 | first occurs at index among the (so ); is |
| 21 | equivariant, has dimension and grows at rate in norm and in slowest |
| 22 | growth; , and grows at rate at least ; is strongly measurable, |
| 23 | tempered, idempotent with range and kernel , and commutes with the cocycle; and |
| 24 | grows at rate , with |
| 25 | . |
| 26 | |
| 27 | These are the stages of the induction by which the decomposition is built in the proof of |
| 28 | Theorem 3 of Lee (2024). |
| 29 | -/ |
| 30 | |
| 31 | namespace Lax606786.OseledetsLevels |
| 32 | |
| 33 | open MeasureTheory Filter Topology |
| 34 | open Lax606786.Cocycles Lax606786.BanachGrassmannian Lax606786.OperatorStatistics |
| 35 | Lax606786.ExtendedLog |
| 36 | |
| 37 | /-- The data of the decomposition after the fast spaces `E_1, …, E_l`: the newest fast space |
| 38 | `E = E_l` (of dimension `m`), their sum `F` (of dimension `M`), the slow space `V`, and the |
| 39 | projection `Q` onto `V` along `F`. -/ |
| 40 | structure LevelData (Ω X : Type*) [NormedAddCommGroup X] [NormedSpace ℝ X] where |
| 41 | M : ℕ |
| 42 | m : ℕ+ |
| 43 | E : Ω → GrassmannianFin X m |
| 44 | F : Ω → GrassmannianFin X M |
| 45 | V : Ω → GrassmannianCofin X M |
| 46 | Q : Ω → X →L[ℝ] X |
| 47 | |
| 48 | /-- `D` is the decomposition after the fast spaces `E_1, …, E_l`, where `lam i` is the `i`-th |
| 49 | distinct exponent. -/ |
| 50 | structure IsLevel {Ω X : Type*} [MeasurableSpace Ω] [StandardBorelSpace Ω] |
| 51 | [NormedAddCommGroup X] [NormedSpace ℝ X] [MeasurableSpace X] |
| 52 | (R : Cocycle Ω X) (lam : ℕ → EReal) (l : ℕ) (D : LevelData Ω X) : Prop where |
| 53 | lambdaIdx_eq : ∀ᵐ ω ∂(R.μ), R.lambdaIdx (l + 1) ω = D.M + 1 |
| 54 | lam_real : ∃ r : ℝ, lam l = r |
| 55 | lam_gap : lam (l + 1) < lam l |
| 56 | Q_meas : ∀ x, Measurable fun ω => D.Q ω x |
| 57 | Q_temp : R.IsTempered D.Q |
| 58 | Q_idem : ∀ᵐ ω ∂(R.μ), (D.Q ω).comp (D.Q ω) = D.Q ω |
| 59 | Q_range : ∀ᵐ ω ∂(R.μ), |
| 60 | LinearMap.range (D.Q ω : X →ₗ[ℝ] X) = ((D.V ω).1.1 : Submodule ℝ X) |
| 61 | Q_ker : ∀ᵐ ω ∂(R.μ), LinearMap.ker (D.Q ω : X →ₗ[ℝ] X) = ((D.F ω).1 : Submodule ℝ X) |
| 62 | Q_equiv : ∀ᵐ ω ∂(R.μ), (D.Q (R.σ ω)).comp (R.L ω) = (R.L ω).comp (D.Q ω) |
| 63 | E_meas : Measurable D.E |
| 64 | E_equiv : ∀ᵐ ω ∂(R.μ), Submodule.map (R.L ω : X →ₗ[ℝ] X) ((D.E ω).1 : Submodule ℝ X) |
| 65 | = ((D.E (R.σ ω)).1 : Submodule ℝ X) |
| 66 | E_dim : ∀ᵐ ω ∂(R.μ), R.mult l ω = D.m |
| 67 | E_norm : ∀ᵐ ω ∂(R.μ), Tendsto (fun n : ℕ => logEReal |
| 68 | ‖(R.iterate n ω).comp (((D.E ω).1 : Submodule ℝ X)).subtypeL‖ / (n : EReal)) atTop |
| 69 | (𝓝 (lam l)) |
| 70 | E_growth : ∀ᵐ ω ∂(R.μ), Tendsto (fun n : ℕ => logEReal |
| 71 | (growth (R.iterate n ω) ((D.E ω).1 : Submodule ℝ X)) / (n : EReal)) atTop (𝓝 (lam l)) |
| 72 | E_le_F : ∀ᵐ ω ∂(R.μ), ((D.E ω).1 : Submodule ℝ X) ≤ ((D.F ω).1 : Submodule ℝ X) |
| 73 | F_growth : ∀ᵐ ω ∂(R.μ), ∀ b : ℝ, (b : EReal) < lam l → ∀ᶠ n : ℕ in atTop, |
| 74 | Real.exp (n * b) ≤ growth (R.iterate n ω) ((D.F ω).1 : Submodule ℝ X) |
| 75 | slow_rate : ∀ᵐ ω ∂(R.μ), Tendsto (fun n : ℕ => |
| 76 | logEReal ‖(R.iterate n ω).comp (D.Q ω)‖ / (n : EReal)) atTop (𝓝 (lam (l + 1))) |
| 77 | slow_char : ∀ᵐ ω ∂(R.μ), |
| 78 | (((D.V ω).1.1 : Submodule ℝ X) : Set X) = {x : X | R.lambdaAt ω x ≤ lam (l + 1)} |
| 79 | |
| 80 | end Lax606786.OseledetsLevels |
| 81 |
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