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The top-level fast/slow decomposition

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

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    Natural Language Statement

    Theorem

    Let L\mathcal{L} be a quasicompact cocycle on a separable Banach space XX with its Borel σ\sigma-algebra, with top exponent λ1∈R\lambda_1 \in \mathbb{R} of multiplicity m1m_1 and second exponent λ2\lambda_2 (possibly −∞-\infty), almost surely. Then there are

    • a fast space E1E_1 of multiplicity m1m_1 at rate λ1\lambda_1, with eventually positive growth;
    • a measurable family of closed complements V(ω)V(\omega) of E1(ω)E_1(\omega) of codimension m1m_1, with LωV(ω)⊆V(σω)\mathcal{L}_\omega V(\omega) \subseteq V(\sigma\omega);
    • strongly measurable, tempered idempotents PωP_\omega with range V(ω)V(\omega) and kernel containing E1(ω)E_1(\omega),

    such that 1nlog⁡∥Lω(n)Pω∥→λ2\frac1n \log \|\mathcal{L}^{(n)}_\omega P_\omega\| \to \lambda_2 almost surely.

    This is Lemma 29 of Lee (2024).

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    Evidence

    In the paper

    • page 12 of this submission's paper

    Lean source view on GitLab

    1import Lax606786.FastSpaces
    2
    3/-!
    4---
    5title: The top-level fast/slow decomposition
    6type: theorem
    7---
    8Let L\mathcal{L} be a quasicompact cocycle on a separable Banach space XX with its Borel
    9σ\sigma-algebra, with top exponent λ1∈R\lambda_1 \in \mathbb{R} of multiplicity m1m_1 and second
    10exponent λ2\lambda_2 (possibly −∞-\infty), almost surely. Then there are
    11
    12- a fast space E1E_1 of multiplicity m1m_1 at rate λ1\lambda_1, with eventually positive growth;
    13- a measurable family of closed complements V(ω)V(\omega) of E1(ω)E_1(\omega) of codimension m1m_1,
    14 with LωV(ω)⊆V(σω)\mathcal{L}_\omega V(\omega) \subseteq V(\sigma\omega);
    15- strongly measurable, tempered idempotents PωP_\omega with range V(ω)V(\omega) and kernel
    16 containing E1(ω)E_1(\omega),
    17
    18such that 1nlog⁡∥Lω(n)Pω∥→λ2\frac1n \log \|\mathcal{L}^{(n)}_\omega P_\omega\| \to \lambda_2 almost surely.
    19
    20This is Lemma 29 of Lee (2024).
    21-/
    22
    23namespace Lax606786.TopDecomposition
    24
    25open MeasureTheory Filter TopologicalSpace
    26open Lax606786.Cocycles Lax606786.BanachGrassmannian Lax606786.OperatorStatistics Lax606786.FastSpaces
    27 Lax606786.ExtendedLog
    28
    29/-- The top fast space, its slow complement and the slow projection. -/
    30axiom topdecomp {Ω X : Type*} [MeasurableSpace Ω] [StandardBorelSpace Ω]
    31 [NormedAddCommGroup X] [NormedSpace ℝ X] [MeasurableSpace X]
    32 (R : Cocycle Ω X) [SeparableSpace X] [BorelSpace X] [CompleteSpace X]
    33 (hqc : R.IsQuasicompact)
    34 (lam : ℝ) (lam2 : EReal) (hlam : ∀ᵐ ω ∂(R.μ), R.chi 1 ω = (lam : EReal))
    35 (hlam2 : ∀ᵐ ω ∂(R.μ), R.lambda 2 ω = lam2) :
    36 ∃ (m1 : ℕ) (_ : NeZero m1) (E : Ω → GrassmannianFin X m1)
    37 (V : Ω → GrassmannianCofin X m1) (P : Ω → X →L[ℝ] X),
    38 (∀ᵐ ω ∂(R.μ), R.mult 1 ω = m1) ∧
    39 IsFastSpace R m1 lam E ∧
    40 (∀ᵐ ω ∂(R.μ), ∀ᶠ n : ℕ in atTop,
    41 0 < growth (R.iterate n ω) ((E ω).1 : Submodule ℝ X)) ∧
    42 (∀ x : X, Measurable fun ω => P ω x) ∧
    43 (∀ᵐ ω ∂(R.μ), (P ω).comp (P ω) = P ω) ∧
    44 (∀ᵐ ω ∂(R.μ), IsCompl ((E ω).1 : Submodule ℝ X) ((V ω).1.1 : Submodule ℝ X)) ∧
    45 (∀ᵐ ω ∂(R.μ), LinearMap.range (P ω : X →ₗ[ℝ] X) = ((V ω).1.1 : Submodule ℝ X) ∧
    46 ∀ e ∈ ((E ω).1 : Submodule ℝ X), P ω e = 0) ∧
    47 (∀ᵐ ω ∂(R.μ), Submodule.map (R.L ω : X →ₗ[ℝ] X) ((V ω).1.1 : Submodule ℝ X)
    48 ≤ ((V (R.σ ω)).1.1 : Submodule ℝ X)) ∧
    49 R.IsTempered P ∧
    50 (∀ᵐ ω ∂(R.μ), Tendsto (fun n : ℕ =>
    51 logEReal ‖(R.iterate n ω).comp (P ω)‖ / (n : EReal)) atTop (nhds lam2))
    52
    53end Lax606786.TopDecomposition
    54
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