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2507.18041

Multifractal analysis of the Lyapunov exponent for random graph directed Markov systems

Yuya Arima

correctmedium confidence
Category
Not specified
Journal tier
Specialist/Solid
Processed
Sep 28, 2025, 12:57 AM

Audit review

The paper proves, under normality, RBSC over finite subedges, and cofinitely regularity, that for a full-measure set of base points ω the Lyapunov level sets satisfy dim_H L_ω(β) = (1/β) inf_s (p(s)+βs) for β in (−p′(+∞), −p′(s_∞)), and are empty outside [−p′(+∞), −p′(s_∞)] (Theorem 1.1). It achieves this via finite-alphabet approximations, a two-parameter pressure, and fiberwise multifractal measures, yielding upper and lower bounds that match (Proposition 4.11, Proposition 4.10, Theorem 4.7, Lemma 4.12). The candidate solution reaches the same conclusion via a standard multifractal formalism: cylinder covers + pressure for the upper bound and random Gibbs/equilibrium measures on finite subsystems for the lower bound, then exhaustion. While the structures and required hypotheses align closely with the paper, the techniques differ in emphasis: the paper builds fiberwise multifractal measures to ensure uniform full-measure sets in s, whereas the model appeals to random RPF/Gibbs arguments and a countable intersection argument over rational s. Both are correct and consistent with each other, but not identical in proof strategy.

Referee report (LaTeX)

\textbf{Recommendation:} minor revisions

\textbf{Journal Tier:} specialist/solid

\textbf{Justification:}

The work establishes a Lyapunov multifractal spectrum formula for random conformal GDMS with countably many branches, combining compact approximations of pressure, fiberwise multifractal measures, and Legendre transforms. The techniques are appropriate and robust for the random setting. The exposition is dense but largely clear; some guidance on the assembly of results into the main theorem would help readers.