pith. sign in

arxiv: 2502.10918 · v3 · submitted 2025-02-15 · ❄️ cond-mat.dis-nn · cond-mat.soft· cond-mat.stat-mech· nlin.PS

Signature of glassy dynamics in dynamic modes decompositions

Pith reviewed 2026-05-23 03:16 UTC · model grok-4.3

classification ❄️ cond-mat.dis-nn cond-mat.softcond-mat.stat-mechnlin.PS
keywords glassy dynamicsdynamic mode decompositionKoopman spectrumalgebraic relaxationcoupled oscillatorsspectral gapdata-driven methods
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The pith

The gap between oscillatory and decaying modes in the Koopman spectrum vanishes in systems with algebraic relaxation, serving as a signature for glassy dynamics.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper applies dynamic mode decomposition to time series data in order to approximate the Koopman spectrum. It shows that this approximation produces no clear separation between oscillatory and decaying modes precisely when the underlying system relaxes algebraically rather than exponentially. The absence of that gap is offered as a general indicator of glassy dynamics that does not depend on knowing the equations or the energy landscape in advance. The claim is checked on a one-dimensional differential equation and on a network of coupled oscillators.

Core claim

The paper claims that the gap between oscillatory and decaying modes in the Koopman spectrum vanishes in systems exhibiting algebraic relaxation. This vanishing gap is therefore proposed as a model-agnostic signature that can be used to detect and analyze glassy dynamics from data alone, and the signature is demonstrated both in a minimal one-dimensional ODE and in a high-dimensional system of coupled oscillators.

What carries the argument

Dynamic mode decomposition, which extracts a finite approximation to the Koopman spectrum (the eigenvalues governing linear evolution of observables) from trajectory data; the central indicator is the disappearance of the gap separating oscillatory from decaying eigenvalues.

If this is right

  • Glassy dynamics can be identified directly from time-series measurements in high-dimensional disordered systems without constructing an explicit model.
  • The same spectral feature distinguishes algebraic relaxation from exponential relaxation across both low- and high-dimensional examples.
  • The approach supplies a practical diagnostic for networks of coupled oscillators that exhibit slow, non-exponential relaxation.
  • The signature remains usable even when the system is far from equilibrium.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same vanishing-gap diagnostic might be applied to time series from other slow-relaxing systems such as trained neural networks or certain biological networks.
  • If the gap disappearance is robust, it could motivate new ways to coarse-grain high-dimensional data when standard spectral gaps are absent.
  • Experimental time series from physical glasses or jammed materials could be re-analyzed with DMD to test whether the signature appears outside the oscillator examples.

Load-bearing premise

Dynamic mode decomposition applied to finite noisy trajectories from disordered high-dimensional systems faithfully approximates the true Koopman spectrum, and the observed vanishing gap is caused by algebraic relaxation rather than by finite-data effects or the choice of observables.

What would settle it

A concrete falsifier would be a system known to relax algebraically whose DMD spectrum on realistic finite noisy data still shows a clear gap, or a system known to relax exponentially whose DMD spectrum shows a vanishing gap under identical data conditions.

Figures

Figures reproduced from arXiv: 2502.10918 by Hangjun Cho, J. Nathan Kutz, Steven L. Brunton, Yuanzhao Zhang, Zachary G. Nicolaou.

Figure 1
Figure 1. Figure 1: FIG. 1. Schematic of Koopman oscillatory (blue) and decay [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. DMD spectrum and pseudospectrum (top panels) and [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Dynamics of three systems of [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. DMD spectra for the three systems in Fig. [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
read the original abstract

Glasses are traditionally characterized by their rugged landscape of disordered low-energy states and their slow relaxation towards thermodynamic equilibrium. Far from equilibrium, dynamical forms of glassy behavior with anomalous algebraic relaxation have also been noted, for example, in networks of coupled oscillators. Due to their disordered and high-dimensional nature, such systems have been difficult to study theoretically, but data-driven methods are emerging as a promising alternative that may aid in their analysis. Here, we characterize glassy dynamics using the dynamic mode decomposition, a data-driven spectral computation that approximates the Koopman spectrum. We show that the gap between oscillatory and decaying modes in the Koopman spectrum vanishes in systems exhibiting algebraic relaxation, and thus, we propose a model-agnostic signature for robustly detecting and analyzing glassy dynamics. We demonstrate the utility of our approach through both a minimal example of a one-dimensional ODE and a high-dimensional example of coupled oscillators.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript proposes that dynamic mode decomposition (DMD) applied to finite trajectories yields a vanishing gap between oscillatory and decaying modes in the approximated Koopman spectrum precisely when the underlying dynamics exhibit algebraic relaxation, thereby furnishing a model-agnostic signature for glassy behavior. The claim is illustrated on a one-dimensional ODE and on a high-dimensional network of coupled oscillators.

Significance. If the signature is shown to be robust against finite-data and noise artifacts, the approach would supply a practical, data-driven diagnostic for detecting algebraic relaxation in high-dimensional disordered systems where traditional analytic tools are limited. The empirical framing on concrete examples is a positive feature.

major comments (2)
  1. [high-dimensional example section] The central claim that the observed vanishing gap is caused by algebraic relaxation rather than by DMD artifacts requires explicit controls (e.g., data-length scaling, noise-level sweeps, and comparison against systems known to relax exponentially). No such controls are described for either the 1D ODE or the coupled-oscillator example; without them the attribution remains unverified.
  2. [DMD application and spectrum analysis] The manuscript does not state how the gap is quantitatively defined or thresholded (e.g., separation in real part of eigenvalues, or a fitted parameter). This definition is load-bearing for the claim that the gap “vanishes” specifically in the algebraic case.
minor comments (1)
  1. Notation for the DMD observables and the precise dictionary used in the high-dimensional example should be stated explicitly.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The two major comments identify genuine gaps in the current manuscript that must be addressed to substantiate the central claim. We will revise the manuscript accordingly and provide the requested controls and definitions.

read point-by-point responses
  1. Referee: [high-dimensional example section] The central claim that the observed vanishing gap is caused by algebraic relaxation rather than by DMD artifacts requires explicit controls (e.g., data-length scaling, noise-level sweeps, and comparison against systems known to relax exponentially). No such controls are described for either the 1D ODE or the coupled-oscillator example; without them the attribution remains unverified.

    Authors: We agree that the absence of these controls leaves the attribution to algebraic relaxation unverified and that DMD artifacts cannot be ruled out on the basis of the presented data alone. In the revised manuscript we will add (i) systematic data-length scaling for both examples, (ii) noise-level sweeps with quantitative metrics of gap stability, and (iii) direct comparisons against reference systems whose relaxation is known to be exponential. These additions will be placed in a new subsection of the high-dimensional example and referenced in the 1D ODE section. revision: yes

  2. Referee: [DMD application and spectrum analysis] The manuscript does not state how the gap is quantitatively defined or thresholded (e.g., separation in real part of eigenvalues, or a fitted parameter). This definition is load-bearing for the claim that the gap “vanishes” specifically in the algebraic case.

    Authors: We acknowledge that the manuscript does not provide an explicit, quantitative definition of the gap or the criterion for declaring it “vanished.” In the revision we will add a precise definition: the gap is the absolute difference between the real parts of the leading oscillatory eigenvalue (imaginary part nonzero) and the leading decaying eigenvalue (imaginary part zero), and we will state the numerical threshold (e.g., gap < 10^{-3}) together with the procedure used to identify the relevant eigenvalues. This definition will be introduced in the Methods section and applied consistently to all figures. revision: yes

Circularity Check

0 steps flagged

No circularity: empirical observation from DMD on example systems

full rationale

The central claim is an empirical observation that the spectral gap vanishes in DMD approximations for systems with algebraic relaxation, demonstrated on a 1D ODE and coupled oscillators. No load-bearing step reduces by construction to a fitted parameter, self-definition, or self-citation chain; the signature is proposed directly from the observed data-driven behavior without mathematical forcing or renaming of known results. The derivation chain is self-contained against external benchmarks as a data-driven proposal.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review supplies no explicit free parameters, axioms, or invented entities.

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discussion (0)

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Reference graph

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    To top row of Fig

    Systems with large N Next, we consider the transition between the exponential and algebraic decay asK and N increase. To top row of Fig. S4 shows ours results at fixed coupling constant J for cases with N ∈ (104, 2 × 104, 105, 2 × 105). We see that for intermediate K/N, there is a kink in the curves signaling a transition between exponential and algebraic...