While this submission is a draft, it cannot be used by other submissions.

The levels of an Oseledets decomposition

Lax606786.OseledetsLevels · concepts/Lax606786/OseledetsLevels.lean · lax-606786

definition

Loading review…

Sign in with ORCID

Community review

Flags

Each flag is tied to a public ORCID identity and explains why this concept may be incorrect.

No flags have been submitted.

    Community review

    Flag this concept

    State precisely what appears incorrect. This explanation will be public under your ORCID name.

    No source line selected.

    Natural Language Statement

    Definition

    Let L\mathcal{L} be a cocycle on a Banach space XX and λ1>λ2>⋯\lambda_1 > \lambda_2 > \cdots its distinct exponents. For l≥1l \ge 1, the decomposition after the first ll fast spaces (level ll) consists of measurable families of

    • the newest fast space E(ω)=El(ω)E(\omega) = E_l(\omega), of dimension m≥1m \ge 1;
    • the sum F(ω)=E1(ω)⊕⋯⊕El(ω)F(\omega) = E_1(\omega) \oplus \cdots \oplus E_l(\omega) of all fast spaces so far, of dimension MM;
    • a slow space V(ω)∈GMXV(\omega) \in \mathcal{G}^M X and a projection Q(ω)Q(\omega) onto V(ω)V(\omega) along F(ω)F(\omega),

    such that, almost surely: λl\lambda_l is real, λl+1<λl\lambda_{l+1} < \lambda_l, and λl+1\lambda_{l+1} first occurs at index M+1M + 1 among the χk\chi_k (so M=m1+⋯+mlM = m_1 + \cdots + m_l); EE is equivariant, has dimension m=mlm = m_l and grows at rate λl\lambda_l in norm and in slowest growth; E⊆FE \subseteq F, and FF grows at rate at least λl\lambda_l; QQ is strongly measurable, tempered, idempotent with range VV and kernel FF, and commutes with the cocycle; and L(n)Q\mathcal{L}^{(n)} Q grows at rate λl+1\lambda_{l+1}, with V(ω)={x:λω(x)≤λl+1}V(\omega) = \{x : \lambda_\omega(x) \le \lambda_{l+1}\}.

    These are the stages of the induction by which the decomposition is built in the proof of Theorem 3 of Lee (2024).

    Concept map
    6 concepts; 2 descendants hidden
    100%
    Proven claimDefinitionThis conceptRelated conceptA → B: B builds on A

    Lean source view on GitLab

    1import Lax606786.Cocycles
    2import Lax606786.BanachGrassmannian
    3
    4/-!
    5---
    6title: The levels of an Oseledets decomposition
    7type: definition
    8---
    9Let L\mathcal{L} be a cocycle on a Banach space XX and λ1>λ2>⋯\lambda_1 > \lambda_2 > \cdots its
    10distinct exponents. For l≥1l \ge 1, the *decomposition after the first ll fast spaces* (level ll)
    11consists of measurable families of
    12
    13- the newest fast space E(ω)=El(ω)E(\omega) = E_l(\omega), of dimension m≥1m \ge 1;
    14- the sum F(ω)=E1(ω)⊕⋯⊕El(ω)F(\omega) = E_1(\omega) \oplus \cdots \oplus E_l(\omega) of all fast spaces so far,
    15 of dimension MM;
    16- a slow space V(ω)∈GMXV(\omega) \in \mathcal{G}^M X and a projection Q(ω)Q(\omega) onto V(ω)V(\omega) along
    17 F(ω)F(\omega),
    18
    19such that, almost surely: λl\lambda_l is real, λl+1<λl\lambda_{l+1} < \lambda_l, and λl+1\lambda_{l+1}
    20first occurs at index M+1M + 1 among the χk\chi_k (so M=m1+⋯+mlM = m_1 + \cdots + m_l); EE is
    21equivariant, has dimension m=mlm = m_l and grows at rate λl\lambda_l in norm and in slowest
    22growth; E⊆FE \subseteq F, and FF grows at rate at least λl\lambda_l; QQ is strongly measurable,
    23tempered, idempotent with range VV and kernel FF, and commutes with the cocycle; and
    24L(n)Q\mathcal{L}^{(n)} Q grows at rate λl+1\lambda_{l+1}, with
    25V(ω)={x:λω(x)≤λl+1}V(\omega) = \{x : \lambda_\omega(x) \le \lambda_{l+1}\}.
    26
    27These are the stages of the induction by which the decomposition is built in the proof of
    28Theorem 3 of Lee (2024).
    29-/
    30
    31namespace Lax606786.OseledetsLevels
    32
    33open MeasureTheory Filter Topology
    34open 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
    39projection `Q` onto `V` along `F`. -/
    40structure 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
    49distinct exponent. -/
    50structure 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
    80end Lax606786.OseledetsLevels
    81

    Discussion

    Ask a question or add context. Endorsements and structured flags are kept in the review panel above.

    Loading discussion…