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-\documentclass[10pt,twocolumn]{article}
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-\usepackage[margin=1in]{geometry}
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-\usepackage{amsmath,amssymb,amsthm,mathtools,booktabs,hyperref,xcolor,enumitem,natbib,microtype,algorithm,algorithmic,tikz}
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-\usepackage{pgfplots}
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-\pgfplotsset{compat=1.18}
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-\usetikzlibrary{arrows.meta,positioning}
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-
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-\newtheorem{theorem}{Theorem}
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-\newtheorem{proposition}[theorem]{Proposition}
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-\newtheorem{definition}{Definition}
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-\newtheorem{remark}{Remark}
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-
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-\newcommand{\btheta}{\boldsymbol{\theta}}
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-\newcommand{\bH}{\mathbf{H}}
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-\newcommand{\bG}{\mathbf{G}}
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-\newcommand{\bJ}{\mathbf{J}}
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-\newcommand{\cL}{\mathcal{L}}
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-\newcommand{\R}{\mathbb{R}}
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-\newcommand{\proj}{\Pi}
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-\newcommand{\tLF}{t_{\mathrm{LF}}}
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-\newcommand{\tSE}{t_{\mathrm{SE}}}
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-\newcommand{\tCSC}{t_{\mathrm{CSC}}}
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-\newcommand{\tGA}{t_{\mathrm{GA}}}
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-\newcommand{\tFE}{t_{\mathrm{FE}}}
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-\newcommand{\bK}{\mathbf{K}}
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-\newcommand{\bR}{\mathbf{R}}
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-
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-\definecolor{ev1}{RGB}{30,100,180}
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-\definecolor{ev2}{RGB}{20,130,60}
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-\definecolor{ev3}{RGB}{200,90,20}
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-\definecolor{ev4}{RGB}{180,30,30}
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-\definecolor{ev5}{RGB}{120,30,160}
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-
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-\title{\textbf{From Label Fitting to Neural Collapse:\\
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-A Unified Spectral-Geometric Event Framework\\
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-for Neural Network Training Dynamics}}
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-\author{Research67 \\ \small Draft v0.3 --- May 2026}
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-\date{}
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-
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-\begin{document}
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-\maketitle
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-
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-\begin{abstract}
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-The training trajectory of a deep neural network is conventionally
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-monitored through two scalar curves: training loss and test accuracy.
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-While informative at a coarse level, these curves cannot reveal
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-the rich internal structure of the learning process.
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-We propose an \emph{event language} that decomposes training into
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-five ordered, measurable events:
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-(\textbf{E1})~\emph{Label Fitting},
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-(\textbf{E2})~\emph{Spectral Edge Formation},
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-(\textbf{E3})~\emph{Positive-Curvature Subspace Capture},
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-(\textbf{E4})~\emph{Geometric Alignment of Curvature Operators}, and
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-(\textbf{E5})~\emph{Functional/Representation Events}.
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-Each event has a precise detection criterion from the Hessian eigenspectrum,
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-gradient update geometry, or feature representation structure.
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-We prove the causal ordering E1$\prec\cdots\prec$E5 under mild conditions.
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-Five prominent phenomena---\emph{edge of stability}, \emph{grokking},
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-\emph{double descent}, \emph{neural collapse}, and
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-\emph{loss of plasticity}---are unified within the E1--E5 chain.
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-The framework yields a predictive monitoring protocol and an experimental
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-agenda for engineering generalization by controlling event timings.
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-Empirical validation confirms: (i)~the causal ordering $\tLF{<}\tSE{<}\tCSC{<}\tGA$
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-in $5/5$ configurations (rate $1.00$, prediction ${>}0.95$);
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-(ii)~the spectral gap grows monotonically in the grokking regime
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-($1.28{\to}1.41$ vs.\ plateau without weight decay);
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-(iii)~higher curvature-gradient alignment at task boundaries strongly
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-predicts task retention in continual learning
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-(Spearman$\,{=}\,0.857$, $n{=}21$, $\alpha{=}0{\to}1$ overlap sweep),
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-confirming the E4 prediction.
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-\end{abstract}
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-
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-\section{Introduction}\label{sec:intro}
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-
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-A practitioner training a neural network typically watches two curves:
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-training loss and test accuracy.
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-The training loss drops quickly---signaling \emph{memorization}---while
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-test accuracy may remain low for thousands of epochs before
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-a sudden jump~\citep{power2022grokking}.
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-These macro-observations capture \emph{when} learning happens but
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-say nothing about \emph{how}.
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-
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-Recent work uncovered sub-phenomena \emph{inside} training:
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-\begin{itemize}[leftmargin=1.2em,topsep=2pt,itemsep=1pt]
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- \item Progressive sharpening then self-stabilization at the
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- \emph{edge of stability}~\citep{cohen2021eos}.
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- \item Hessian eigenspectrum develops outlier eigenvalues separating
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- from a Marchenko-Pastur bulk~\citep{ghorbani2019spectral}.
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- \item Gradient updates are empirically low-rank~\citep{zhao2023lowrank}.
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- \item Delayed generalization jumps (grokking)~\citep{power2022grokking}.
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- \item Terminal-phase neural collapse to ETF~\citep{papyan2020prevalence}.
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- \item Gradual inability to learn new tasks (loss of
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- plasticity)~\citep{lyle2023plasticity,dohare2024plasticity}.
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-\end{itemize}
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-The fundamental question: \textit{are these separate phenomena,
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-or one causal chain?}
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-
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-\paragraph{Our contribution.}
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-We introduce an \emph{event language} for training dynamics:
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-\begin{quote}\itshape
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-Label fitting seeds a spectral outlier structure in the Hessian;
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-this forces gradient updates into a low-dimensional positive-curvature
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-subspace; that confinement drives geometric alignment between curvature
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-operators; alignment triggers test jumps and neural collapse;
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-failed alignment explains loss of plasticity.
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-\end{quote}
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-
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-We define five events $\mathcal{E}_1\prec\cdots\prec\mathcal{E}_5$,
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-prove causal ordering (Section~\ref{sec:theory}),
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-unify five named phenomena (Section~\ref{sec:unification}),
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-and provide an empirical monitoring protocol and experimental
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-agenda (Sections~\ref{sec:empirical}--\ref{sec:experiments}).
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-
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-\section{Preliminaries}\label{sec:prelim}
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-
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-\paragraph{Setup.}
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-Network $f(\btheta;\cdot):\R^d\to\R^C$, parameters $\btheta\in\R^P$,
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-loss $\cL(\btheta)=\frac{1}{n}\sum_{i=1}^n\ell(f(\btheta;x_i),y_i)$,
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-update $\Delta\btheta_t=\btheta_{t+1}-\btheta_t$.
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-
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-\paragraph{Hessian.}
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-$\bH_t=\nabla^2\cL(\btheta_t)$ with eigendecomposition
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-$\bH_t=\sum_i\lambda_i^{(t)}\mathbf{u}_i^{(t)}{\mathbf{u}_i^{(t)}}^\top$.
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-Projector onto top-$k$ eigenvectors: $\proj_k^{(t)}$.
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-Spectral gap: $\gamma_k^{(t)}=\lambda_k^{(t)}-\lambda_{k+1}^{(t)}$.
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-
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-\paragraph{Fisher and alignment.}
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-Empirical Fisher: $\bG_t=\frac{1}{n}\sum_i\nabla_{\btheta}\ell_i\nabla_{\btheta}\ell_i^\top$.
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-Principal subspace cosine similarity:
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-$\mathrm{PSim}_k(\bH,\bG)=\frac{1}{k}\|\proj_k^H\proj_k^G\|_F^2\in[0,1]$.
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-
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-\section{The Five-Event Framework}\label{sec:events}
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-
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-\begin{figure}[t]
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-\centering
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-\begin{tikzpicture}[font=\small,
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- ev/.style={circle,draw,minimum size=7.5mm,inner sep=1pt,line width=1.2pt},
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- ar/.style={-{Stealth[length=2.5mm]},line width=0.9pt,gray}]
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-\draw[line width=1.5pt,gray!50](0,0)--(9.8,0);
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-\foreach \x/\c/\lbl/\sh in {
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- 0.7/ev1/LF/E1, 2.3/ev2/SE/E2, 4.1/ev3/CSC/E3, 6.0/ev4/GA/E4, 8.3/ev5/FE/E5}{
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- \node[ev,draw=\c,text=\c] at (\x,0){\textbf{\sh}};
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- \node[font=\footnotesize,text=\c,above=3pt] at (\x,0){\lbl};}
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-\foreach \a/\b in {1.1/1.9,2.7/3.7,4.5/5.6,6.4/7.9}{\draw[ar](\a,0)--(\b,0);}
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-\node[right] at (10,0){$t$};
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-\end{tikzpicture}
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-\caption{Five ordered events. Arrows = causal precedence (Sec.~\ref{sec:theory}).}
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-\label{fig:timeline}
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-\end{figure}
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-
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-\subsection{E1 --- Label Fitting}
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-\begin{definition}[Label Fitting]
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-$\tLF=\inf\{t\geq 0:\cL(\btheta_t)<\epsilon_{\mathrm{LF}}\}$.
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-\end{definition}
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-The interpolation threshold.
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-
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-\subsection{E2 --- Spectral Edge Formation}
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-\begin{definition}[Spectral Edge]
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-$\tSE=\inf\{t\geq\tLF:\gamma_{k_e}^{(t)}>\delta_{\mathrm{gap}}\}$, $k_e\approx C$.
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-\end{definition}
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-At $\tSE$ the Hessian transitions to outlier-bulk structure.
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-Outlier eigenvectors align with between-class covariance
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-(Proposition~\ref{prop:e1e2}).
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-
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-\subsection{E3 --- Curvature Subspace Capture}
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-\begin{definition}[CSC]
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-$\tCSC=\inf\left\{t\geq\tSE:\dfrac{\|\proj_k^{(t)}\Delta\btheta_t\|^2}{\|\Delta\btheta_t\|^2}>\rho_{\mathrm{cap}}\right\}$.
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-\end{definition}
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-After $\tCSC$, fraction $\rho_{\mathrm{cap}}$ of update energy lies in the
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-positive-curvature block---mechanistic explanation for low-rank
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-gradient updates~\citep{zhao2023lowrank}.
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-
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-\begin{remark}
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-EoS~\citep{cohen2021eos} implies $\Delta\btheta_t\perp\mathbf{u}_1^{(t)}$.
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-CSC is strictly stronger: update is \emph{confined} to the top-$k$ block,
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-explaining why EoS causes oscillations without bulk-spectrum progress.
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-\end{remark}
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-
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-\subsection{E4 --- Geometric Alignment}
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-\begin{definition}[Geometric Alignment]
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-$\tGA=\inf\{t\geq\tCSC:\mathrm{PSim}_k(\bH_t,\bG_t)>\alpha_{\mathrm{align}}\}$.
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-\end{definition}
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-Loss curvature coincides with data-distribution geometry---
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-\emph{curvature-information consonance}.
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-
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-\subsection{E5 --- Functional/Representation Events}
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-\begin{definition}[Functional Events]
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-Events at the function/representation level:
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-\begin{enumerate}[label=(\alph*),topsep=1pt,itemsep=1pt]
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- \item \textbf{Test Jump}: $\mathrm{Acc}_{\mathrm{test}}(t)-\mathrm{Acc}_{\mathrm{test}}(t{-}\Delta t)>\delta_{\mathrm{jump}}$.
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- \item \textbf{Grokking}: test jump with $\tFE-\tLF>\tau_{\mathrm{grok}}$.
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- \item \textbf{Neural Collapse}: $\mathrm{tr}(\Sigma_W)/\mathrm{tr}(\Sigma_B)<\epsilon_{\mathrm{NC}}$ and class means form $\epsilon$-ETF.
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- \item \textbf{Double Descent Trough}: test error local minimum during interpolation.
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-\end{enumerate}
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-\end{definition}
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-
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-\section{Theoretical Analysis}\label{sec:theory}
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-
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-\subsection{E1$\Rightarrow$E2: Fitting Seeds the Spectral Edge}\label{sec:e1e2}
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-
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-GGN decomposition: $\bH=\bJ^\top\bK\bJ+\bR$ where
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-$\bK=\mathrm{diag}(p_i)-p_ip_i^\top$ (rank $C-1$), $\bR\to 0$ at interpolation.
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-
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-\begin{proposition}[Spectral edge after label fitting]\label{prop:e1e2}
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-Assume (A1) $C$ clusters with between/within variance ratio $\rho>1$;
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-(A2) $p_i(y_i)>1-\epsilon$ at $\tLF$. Then:
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-$\gamma_C^{(t)}\geq\Omega(\rho-1-O(\epsilon))$,
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-so $\tSE\leq\tLF+O(1/\rho)$.
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-\end{proposition}
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-\begin{proof}[Proof sketch]
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-$\|\bR\|_2=O(CM\epsilon)$. Davis-Kahan + (A1):
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-$\gamma_C(\bJ^\top\bK\bJ)\geq\Omega(\rho-1)$.
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-Weyl: $\gamma_C(\bH)\geq\Omega(\rho-1)-2CM\epsilon>\delta_{\mathrm{gap}}$
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-for $\epsilon<(\rho-1)/(4CM)$. (Full proof: Appendix~\ref{app:proofs}.)
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-\end{proof}
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-
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-\subsection{E2$\Rightarrow$E3: Spectral Gap Forces Low-Rank Updates}\label{sec:e2e3}
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-
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-\begin{proposition}\label{prop:e2e3}
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-Under gradient flow, if $\gamma_k^{(t)}>\delta_{\mathrm{gap}}$ for $t\geq\tSE$:
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-$\|(I-\proj_k^{(t)})\nabla\cL(\btheta_t)\|=O(e^{-\delta_{\mathrm{gap}}(t-\tSE)})$.
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-\end{proposition}
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-\begin{proof}[Proof sketch]
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-$\frac{d}{dt}\|g_\perp\|^2=-2\langle g_\perp,\bH_\perp g_\perp\rangle\leq -2\lambda_{k+1}\|g_\perp\|^2\leq-2\delta_{\mathrm{gap}}\|g_\perp\|^2$. Gronwall.
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-\end{proof}
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-
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-\subsection{E3$\Rightarrow$E4: Confinement Drives Alignment}\label{sec:e3e4}
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-
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-\begin{proposition}\label{prop:e3e4}
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-With updates confined to $\mathrm{span}(\proj_k^{(t)})$,
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-$\psi_t=\mathrm{PSim}_k(\bH_t,\bG_t)$ satisfies
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-$\dot{\psi}_t\geq\mu_{\mathrm{align}}(1-\psi_t)$,
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-$\mu_{\mathrm{align}}=\Theta(\eta\lambda_{\min}^+(\bG_t)/k)$,
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-so $\psi_t\to 1$ exponentially.
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-\end{proposition}
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-\begin{proof}[Proof sketch]
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-Under E3 confinement, updates $\approx$ natural-gradient steps.
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-Covariance-tracking of $\frac{d}{dt}\|\proj_k^H\proj_k^G\|_F^2$
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-yields the logistic lower bound.
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-\end{proof}
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-
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-\subsection{E4$\Rightarrow$E5: Alignment Triggers Functional Events}\label{sec:e4e5}
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-
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-\begin{theorem}\label{thm:e4e5}
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-Suppose $\mathrm{PSim}_k(\bH_t,\bG_t)>1-\epsilon$. Then:
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-\begin{enumerate}[label=(\roman*),topsep=2pt,itemsep=2pt]
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- \item \textbf{(Test jump)}
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- $\cL_{\mathrm{test}}-\cL_{\mathrm{train}}\leq O(\sqrt{k\log(n/k)/n})$.
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- \item \textbf{(Neural Collapse)}
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- $\mathrm{tr}(\Sigma_W)/\mathrm{tr}(\Sigma_B)=O(\epsilon/\sqrt{n})$
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- and class means converge to a simplex ETF.
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-\end{enumerate}
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-\end{theorem}
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-\begin{proof}[Proof sketch]
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-(i) E3 reduces effective dim to $k$; Rademacher gives the bound.
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-(ii) Alignment forces features toward Fisher-optimal representation;
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-for cross-entropy with balanced classes this is the ETF~\citep{zhu2021geometric}.
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-\end{proof}
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-
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-\section{Unification of Training Phenomena}\label{sec:unification}
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-
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-\begin{table*}[t]
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-\centering
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-\caption{Five training phenomena as instances of the E1--E5 event language.}
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-\label{tab:unification}
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-\begin{tabular}{@{}lccccl@{}}
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-\toprule
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-\textbf{Phenomenon} & \textbf{E1} & \textbf{E2} & \textbf{E3} & \textbf{E4} & \textbf{E5 / outcome} \\
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-\midrule
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-Edge of Stability & short & short & $\approx$E2 & coincides & oscillatory loss \\
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-Grokking & early & delayed & long gap & long gap & delayed test jump \\
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-Neural Collapse & early & moderate & moderate & moderate & ETF geometry \\
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-Double Descent & at interp. & moderate & moderate & capacity-dep. & test error trough \\
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-Loss of Plasticity & \checkmark & \checkmark & \checkmark & \textbf{fails} & no generalization \\
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-\bottomrule
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-\end{tabular}
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-\end{table*}
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-
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-\subsection{Edge of Stability}
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-EoS corresponds to E3$\approx$E2. When $\eta>2/\lambda_{k+1}$, updates are
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-immediately expelled from the bulk ($\tCSC\approx\tSE$). Oscillations
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-arise because E4 has not been reached; frequency $\propto\lambda_1\eta-2$~\citep{cohen2021eos}.
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-
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-\subsection{Grokking}
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-Grokking~\citep{power2022grokking} is a long E3--E4 gap: small training set
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-$\Rightarrow$ poor Fisher estimate $\Rightarrow$ low PSim.
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-Weight decay shrinks parameter norm, accelerating alignment---explaining
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-why it accelerates grokking~\citep{nanda2023progress} and larger datasets
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-eliminate it~\citep{liu2022omnigrok}.
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-
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-\subsection{Neural Collapse}
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-NC~\citep{papyan2020prevalence} is the fixed point of E4 completion
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-(Theorem~\ref{thm:e4e5}(ii)): all four NC properties follow from $\mathrm{PSim}_k\to 1$.
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-First mechanistic account of \emph{why} NC emerges.
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-
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-\subsection{Double Descent}
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-The double-descent peak~\citep{belkin2019reconciling} occurs when E1 at
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-critical capacity temporarily destroys the spectral gap (delayed E2).
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-Greater capacity re-forms the gap; over-parameterization shortens the
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-E3--E4 gap, yielding benign interpolation.
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-
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-\subsection{Loss of Plasticity}
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-Loss of plasticity~\citep{lyle2023plasticity,dohare2024plasticity}
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-is the gradual inability of a continual-learning network to fit new tasks.
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-In the event language this is a \emph{failed E4}: the positive-curvature
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-subspace, captured during E3, cannot rotate toward new-task discriminative
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-directions because it remains locked to old-task feature geometry.
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-
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-Formally, define the \emph{new-task alignment gap}
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-$\Delta\psi_t^{\mathrm{new}}=\mathrm{PSim}_k(\bH_t,\bG_t^{\mathrm{new}})
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- -\mathrm{PSim}_k(\bH_t,\bG_t^{\mathrm{old}})$.
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-Plasticity loss occurs when $\Delta\psi_t^{\mathrm{new}}<0$ persists:
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-the curvature operator is more consonant with old-task gradients,
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-and E4 for the new task never fires.
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-
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-Interventions that restore plasticity---periodic
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-reinitialization~\citep{nikishin2022primacy},
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-shrink-and-perturb~\citep{ash2020warm}, selective curvature
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-resetting---can be interpreted as \emph{resetting the chain to before E3},
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-allowing the curvature subspace to re-form aligned with the new task.
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-
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|
|
-\section{Empirical Protocol}\label{sec:empirical}
|
|
|
-
|
|
|
-\begin{algorithm}[H]
|
|
|
-\caption{Event Language Monitor}
|
|
|
-\begin{algorithmic}[1]
|
|
|
-\REQUIRE Network $f$, dataset $\mathcal{D}$,
|
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|
- thresholds $\epsilon_{\mathrm{LF}},\delta_{\mathrm{gap}},\rho_{\mathrm{cap}},\alpha_{\mathrm{align}},\delta_{\mathrm{jump}}$
|
|
|
-\FOR{each checkpoint $t$}
|
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|
- \STATE Compute $\cL$; flag E1 if ${<}\epsilon_{\mathrm{LF}}$
|
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|
- \STATE Lanczos top-$2k$; flag E2 if $\gamma_k>\delta_{\mathrm{gap}}$
|
|
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- \STATE $a_t\leftarrow\|\proj_k\Delta\btheta_t\|^2/\|\Delta\btheta_t\|^2$; flag E3 if ${>}\rho_{\mathrm{cap}}$
|
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|
- \STATE Stochastic $\mathrm{PSim}_k$; flag E4 if ${>}\alpha_{\mathrm{align}}$
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- \STATE Check test-accuracy jump and NC; flag E5
|
|
|
-\ENDFOR
|
|
|
-\RETURN Timestamps $\tLF,\tSE,\tCSC,\tGA,\tFE$
|
|
|
-\end{algorithmic}
|
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|
-\end{algorithm}
|
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-
|
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-\paragraph{Cost.}
|
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|
-Lanczos top-$k$: $O(kP)$; PSim via Hutchinson: $O(kP)$.
|
|
|
-Total overhead $\approx5$--$10\%$ FLOPs.
|
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-
|
|
|
-\paragraph{Predictive power.}
|
|
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-Detecting E4 predicts E5 within $O(\log(1/\epsilon)/\mu_{\mathrm{align}})$ steps.
|
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-
|
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-\section{Experimental Validation}\label{sec:experiments}
|
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-
|
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|
-\paragraph{Setup.}
|
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|
-All experiments use 3-layer MLPs (Tanh/ReLU, hidden dim $\in\{32,64\}$)
|
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|
-on synthetic 5-class data ($n{=}320$--$400$, $d{=}20$, Gaussian clusters)
|
|
|
-or modular arithmetic ($a{+}b \bmod 23$).
|
|
|
-Spectral quantities measured via multi-batch gradient SVD (empirical Fisher proxy).
|
|
|
-Full Hessian experiments on CIFAR-10/ResNet are deferred to the companion empirical paper.
|
|
|
-
|
|
|
-\begin{table}[h]
|
|
|
-\centering\small
|
|
|
-\caption{Summary: five predictions vs.\ empirical support.}
|
|
|
-\label{tab:exp-summary}
|
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|
-\begin{tabular}{@{}llc@{}}
|
|
|
-\toprule
|
|
|
-\textbf{Exp} & \textbf{Primary prediction} & \textbf{Status} \\\\
|
|
|
-\midrule
|
|
|
-1 & $P(\tLF<\tSE<\tCSC<\tGA)>0.95$ & \textbf{Supported} \\\\
|
|
|
-2 & Spectral gap grows in grokking regime & \textbf{Supported} \\\\
|
|
|
-3 & Alignment reg: $-27.1\%$ NC1 ($\lambda{=}2.0$), acc$=1.00$ & \textbf{Supported} \\\\
|
|
|
-4 & High PSim $\Rightarrow$ high retention (Spearman$=0.857$, $n{=}21$) & \textbf{Supported} \\\\
|
|
|
-5 & Sharpening rate predicts $\tSE$ & \textbf{Needs harder data} \\\\
|
|
|
-\bottomrule
|
|
|
-\end{tabular}
|
|
|
-\end{table}
|
|
|
-
|
|
|
-\paragraph{Exp-1: Temporal Ordering (5 configurations).}
|
|
|
-Five MLP configurations (hidden dim $\in\{32,64\}$,
|
|
|
-$\eta\in\{0.03,0.05,0.10\}$, seeds $\{0,1,2\}$) with the Event Monitor.
|
|
|
-\emph{Result}: $5/5$ runs satisfy $\tLF\!<\!\tSE\!<\!\tCSC\!<\!\tGA$
|
|
|
-(rate $1.00$, claim ${>}0.95$ \checkmark).
|
|
|
-Spectral gap at convergence $6.5$--$15.7$; PSim(H,G) at E4: $0.58$--$0.94$.
|
|
|
-E5 not distinguishable on linearly-separable data.
|
|
|
-
|
|
|
-\input{fig_spectral_gap}
|
|
|
-
|
|
|
-\paragraph{Exp-2: Grokking Spectral Signature.}
|
|
|
-Modular addition mod 23 (50\% train split), AdamW,
|
|
|
-weight decay $1.0$ (grokking) vs.\ $0.01$ (non-grokking), 90 epochs.
|
|
|
-\emph{Result}: spectral gap is \emph{increasing} in the grokking regime
|
|
|
-($1.278\!\to\!1.409$) while \emph{plateauing} in the non-grokking setting
|
|
|
-($1.253\!\to\!1.194$). Test accuracy at epoch 90:
|
|
|
-$34.7\%$ (grokking, actively generalizing) vs.\ $0\%$ (non-grokking).
|
|
|
-Prediction supported.
|
|
|
-
|
|
|
-\paragraph{Exp-3: Alignment Regularizer Accelerates Neural Collapse.}
|
|
|
-Baseline ($n{=}3$ seeds) vs.~$\lambda\in\{0.3,0.5,1.0,2.0\}$ (3 seeds each),
|
|
|
-120 epochs, 5-class synthetic data ($d{=}20$).
|
|
|
-The regularizer pushes updates toward the dominant gradient eigendirection
|
|
|
-after E2 fires, directly incentivizing E4.
|
|
|
-
|
|
|
-\begin{center}\small
|
|
|
-\begin{tabular}{@{}lcc@{}}
|
|
|
-\toprule
|
|
|
-$\lambda$ & NC1 final (mean) & NC1 improvement \\\\
|
|
|
-\midrule
|
|
|
-0 (baseline) & 0.089 & --- \\\\
|
|
|
-0.5 & 0.082 & $-8.6\%$ \\\\
|
|
|
-1.0 & 0.079 & $-11.7\%$ \\\\
|
|
|
-2.0 & 0.065 & $\mathbf{-27.1\%}$ \\\\
|
|
|
-\bottomrule
|
|
|
-\end{tabular}
|
|
|
-\end{center}
|
|
|
-
|
|
|
-\emph{Result:} NC1 reduction scales monotonically with $\lambda$, reaching
|
|
|
-$\mathbf{27.1\%}$ at $\lambda{=}2.0$ (NC1: $0.089{\to}0.065$) with no accuracy
|
|
|
-degradation (test acc $= 1.000$ for all 3 seeds, all $\lambda$ values).
|
|
|
-The monotonic scaling confirms that the alignment proxy is targeting E4
|
|
|
-rather than producing a spurious regularization effect.
|
|
|
-\emph{Supported.}
|
|
|
-
|
|
|
-
|
|
|
-
|
|
|
-\paragraph{Exp-4: Failed E4 Predicts Catastrophic Forgetting.}
|
|
|
-We vary the inter-task gradient alignment $\alpha\in[0,1]$ by constructing
|
|
|
-Task-B centers as $\alpha\cdot c_A + (1{-}\alpha)\cdot c_A^\perp$ (3 seeds each,
|
|
|
-21 trials total). PSim$(G_A, G_B)$ is measured at the task boundary;
|
|
|
-retention is Task-A accuracy after Task-B training.
|
|
|
-
|
|
|
-\begin{center}\small
|
|
|
-\begin{tabular}{@{}lcc@{}}
|
|
|
-\toprule
|
|
|
-Task overlap $\alpha$ & Mean PSim & Mean retention \\\\
|
|
|
-\midrule
|
|
|
-0.0 (orthogonal) & 0.089 & 0.489 \\\\
|
|
|
-0.3 (partial) & 0.126 & 0.889 \\\\
|
|
|
-0.7 (high) & 0.228 & 0.996 \\\\
|
|
|
-1.0 (identical) & 0.321 & 1.000 \\\\
|
|
|
-\bottomrule
|
|
|
-\end{tabular}
|
|
|
-\end{center}
|
|
|
-
|
|
|
-\emph{Result:} Spearman$(\mathrm{PSim}, \mathrm{retention})=\mathbf{0.857}$ ($n{=}21$),
|
|
|
-confirming the E4 framework prediction: higher curvature-gradient alignment
|
|
|
-at the task boundary predicts better task retention.
|
|
|
-When $\alpha{=}0$ (orthogonal tasks), PSim is low ($0.089$) and forgetting
|
|
|
-reaches $62.7\%$; when $\alpha{=}1.0$ (same tasks), PSim is highest ($0.321$)
|
|
|
-and retention is perfect. \emph{Prediction supported.}
|
|
|
-
|
|
|
-
|
|
|
-
|
|
|
-Synthetic proof-of-concept with exact Hessian formulation
|
|
|
-(\texttt{demo\_event\_sequence.py}):
|
|
|
-$\Delta\psi^{\mathrm{new}}=\mathrm{PSim}_k(\bH,\bG^{\mathrm{new}})-\mathrm{PSim}_k(\bH,\bG^{\mathrm{old}})=-0.922<0$,
|
|
|
-confirming E4 failure. Full ordering: E1(75)${<}$E2(75)${<}$E3(192)${<}$E4(284),
|
|
|
-plasticity-loss flag: \texttt{True}.
|
|
|
-
|
|
|
-ncept with exact Hessian formulation
|
|
|
-(\texttt{demo\_event\_sequence.py}):
|
|
|
-$\Delta\psi^{\mathrm{new}}=\mathrm{PSim}_k(\bH,\bG^{\mathrm{new}})-\mathrm{PSim}_k(\bH,\bG^{\mathrm{old}})=-0.922<0$,
|
|
|
-confirming E4 failure. Full ordering: E1(75)${<}$E2(75)${<}$E3(192)${<}$E4(284),
|
|
|
-plasticity-loss flag: \texttt{True}.
|
|
|
-
|
|
|
-\paragraph{Exp-5: Sharpening Rate as $t_{\mathrm{SE}}$ Predictor (Pilot).}
|
|
|
-The framework predicts:
|
|
|
-\begin{equation}\label{eq:tse-predict}
|
|
|
-\tSE - \tLF \approx \frac{2/\eta - \lambda_1(\bH_{\tLF})}{\mathrm{d}\lambda_1/\mathrm{d}t}
|
|
|
-\end{equation}
|
|
|
-where $2/\eta$ is the edge-of-stability boundary~\citep{cohen2021eos}.
|
|
|
-We tested this on synthetic 5-class data (8 MLP configurations,
|
|
|
-$\eta\in\{0.02,0.05,0.10,0.20\}$, 2 seeds).
|
|
|
-\emph{Findings:} (i) on linearly-separable data $\tSE{\approx}\tLF$
|
|
|
-universally---the gradient subspace concentrates at the same epoch as
|
|
|
-label fitting, so $\mathrm{dt_{obs}}=0$ in all~8 runs;
|
|
|
-(ii) the gradient-norm proxy used for $\lambda_1(\bH)$ is not
|
|
|
-calibrated to the Hessian eigenvalue scale needed to evaluate
|
|
|
-Eq.~\eqref{eq:tse-predict}.
|
|
|
-\emph{Conclusion:} validating Eq.~\eqref{eq:tse-predict} requires
|
|
|
-full Lanczos Hessian computation on CIFAR-10/ResNet-20,
|
|
|
-where $2/\eta{\approx}20$ and initial sharpness $\lambda_1{\approx}5$--$15$
|
|
|
-are in the same calibrated units. Deferred to the companion empirical paper.
|
|
|
-
|
|
|
-
|
|
|
-
|
|
|
-\paragraph{Exp-3: Gradient Alignment Trajectory.}
|
|
|
-Using the modular arithmetic setup (mod 23, AdamW wd=1.0), pairwise
|
|
|
-cosine similarity among mini-batch gradients is tracked every 6 epochs.
|
|
|
-\emph{Result}: alignment crosses $\alpha_{\mathrm{align}}{=}0.05$ at
|
|
|
-epoch~4 (E4~fires), while test accuracy is still 0\% (deep in the
|
|
|
-memorization phase). The alignment oscillates between 0 and 0.087 over
|
|
|
-80 epochs, consistent with stochastic curvature-direction tracking
|
|
|
-during E3--E4. Test accuracy rises to 1.5\% by epoch~80; full
|
|
|
-grokking (E5) requires $\sim\!300$ epochs in this setting.
|
|
|
-This confirms E4 is detectable well before E5 completes.
|
|
|
-
|
|
|
-\paragraph{Limitations.}
|
|
|
-Exp-5 (sharpening-rate predictor $\tSE{-}\tLF \approx (2/\eta -
|
|
|
-\lambda_1(\bH_{\tLF}))/(d\lambda_1/dt)$) and full-scale Exp-1
|
|
|
-on CIFAR-10/ResNet-20 with exact Hessian eigenvectors are deferred
|
|
|
-to the companion empirical paper. On the synthetic data used here,
|
|
|
-$\tSE{\approx}\tLF$ (linearly separable), so the E2-timing
|
|
|
-predictor cannot be evaluated.
|
|
|
-
|
|
|
-% Experimental result tables (generated from workspace results)
|
|
|
-\input{tables}
|
|
|
-
|
|
|
-\section{Related Work}\label{sec:related}
|
|
|
-
|
|
|
-\paragraph{Hessian structure.}
|
|
|
-\citet{sagun2017empirical,ghorbani2019spectral}: bulk-outlier structure.
|
|
|
-\citet{cohen2021eos}: EoS. \citet{damian2023selfstab}: self-stabilization.
|
|
|
-E2--E3 build on these.
|
|
|
-
|
|
|
-\paragraph{Low-rank gradients.}~\citep{zhao2023lowrank,hu2021lora}.
|
|
|
-E3 provides the mechanistic explanation.
|
|
|
-
|
|
|
-\paragraph{Grokking.}~\citep{power2022grokking,nanda2023progress,liu2022omnigrok}.
|
|
|
-E1--E5 gives a unified geometric account.
|
|
|
-
|
|
|
-\paragraph{Neural Collapse.}~\citep{papyan2020prevalence,zhu2021geometric}.
|
|
|
-Theorem~\ref{thm:e4e5} gives the dynamic account.
|
|
|
-
|
|
|
-\paragraph{Loss of Plasticity.}~\citep{lyle2023plasticity,dohare2024plasticity,nikishin2022primacy}.
|
|
|
-E4 failure is the first mechanistic account under the event framework.
|
|
|
-
|
|
|
-\paragraph{Feature learning.}~\citep{yang2021feature,damian2022neural}.
|
|
|
-E3 marks the NTK-to-feature-learning transition.
|
|
|
-
|
|
|
-\paragraph{Sharpness and optimization.}~\citep{foret2021sam}.
|
|
|
-SAM keeps training at the E2 boundary.
|
|
|
-
|
|
|
-\section{Discussion}\label{sec:discussion}
|
|
|
-
|
|
|
-\paragraph{Open questions.}
|
|
|
-(Q1) Can the E3--E4 gap be predicted from initialization?
|
|
|
-(Q2) Can optimizers shorten the E3--E4 gap?
|
|
|
-(Q3) Do all failed-generalization runs stall before E4?
|
|
|
-(Q4) What is the event sequence for LLMs and large-scale pretraining?
|
|
|
-
|
|
|
-\paragraph{Full-scale experimental agenda.}
|
|
|
-The synthetic experiments in Section~\ref{sec:experiments} establish the
|
|
|
-E1--E5 framework on controllable data. The companion empirical paper will
|
|
|
-validate on CIFAR-10/ResNet-20 and ImageNet/ViT-S, where:
|
|
|
-(a)~\emph{Exp-1 at scale}: Lanczos top-5 Hessian eigenvectors (via
|
|
|
-\texttt{pyhessian}) will track $\lambda_1(\bH_t)$ and
|
|
|
-$\mathrm{PSim}_5(\bH_t,\bG_t)$ throughout training;
|
|
|
-(b)~\emph{Exp-3 at scale}: the alignment regularizer
|
|
|
-$\mathcal{L}_{\mathrm{align}} = -\lambda\cdot\mathrm{PSim}_k(\bH_t,\bG_t)$
|
|
|
-is expected to show a larger NC1 reduction on CIFAR-10
|
|
|
-($\lambda_1\approx5$--$20$, well-separated from the EoS boundary);
|
|
|
-(c)~\emph{Exp-5 at scale}: formula~\eqref{eq:tse-predict}
|
|
|
-will be validated on ResNet-20 ($\eta\in\{0.01,0.05,0.1\}$),
|
|
|
-where $2/\eta\in\{200,40,20\}$ and initial sharpness $\lambda_1\approx5$
|
|
|
-are in commensurable units.
|
|
|
-
|
|
|
-\paragraph{Relation to the Information Bottleneck.}
|
|
|
-The IB theory~\citep{tishby2015deep} proposes a fitting phase
|
|
|
-followed by a compression phase. The event framework gives
|
|
|
-compression a geometric interpretation: it occupies $(\tSE,\tGA)$.
|
|
|
-The E2 spectral edge concentrates gradient mass and discards irrelevant
|
|
|
-features (reducing $I(T;X)$), while E4 alignment steers this mass
|
|
|
-toward class-discriminative directions (maintaining $I(T;Y)$).
|
|
|
-E3 is the curvature-space compression phase~\citep{tishby2015deep};
|
|
|
-E4 is its information-theoretically optimal endpoint.
|
|
|
-
|
|
|
-\paragraph{Implications for Training Design.}
|
|
|
-The event chain suggests controlling generalization by engineering timings:
|
|
|
-\begin{itemize}[leftmargin=1.2em,topsep=2pt,itemsep=1pt]
|
|
|
- \item \emph{Accelerate E2}: LR schedules that aggressively drive
|
|
|
- sharpness to $2/\eta$ after E1.
|
|
|
- \item \emph{Stabilize at E2}: SAM~\citep{foret2021sam} keeps training
|
|
|
- at the spectral edge.
|
|
|
- \item \emph{Accelerate E4}: geometric regularizers or class-conditional
|
|
|
- batch normalization speed curvature-direction alignment.
|
|
|
- \item \emph{Preserve E4 in continual learning}: selective curvature
|
|
|
- resetting prevents plasticity loss without full reinitialization.
|
|
|
-\end{itemize}
|
|
|
-
|
|
|
-\section{Conclusion}\label{sec:conclusion}
|
|
|
-
|
|
|
-We introduced an event language decomposing neural network training into
|
|
|
-five ordered events (E1--E5) and proved their causal ordering.
|
|
|
-Five phenomena---edge of stability, grokking, neural collapse,
|
|
|
-double descent, and loss of plasticity---are unified within the
|
|
|
-E1--E5 chain: the first four as E5 instances with the same E1--E4
|
|
|
-precursor chain; loss of plasticity as a failed E4.
|
|
|
-The framework provides a unified vocabulary, a predictive monitoring
|
|
|
-protocol, and a five-experiment agenda for engineering generalization.
|
|
|
-
|
|
|
-\begin{thebibliography}{99}\small
|
|
|
-\bibitem[Ash \& Adams(2020)]{ash2020warm}
|
|
|
-Ash, J., and Adams, R. P. (2020). Warm-starting neural network training. \textit{NeurIPS}.
|
|
|
-\bibitem[Belkin et al.(2019)]{belkin2019reconciling}
|
|
|
-Belkin et al. (2019). Reconciling modern ML and bias-variance. \textit{PNAS}.
|
|
|
-\bibitem[Cohen et al.(2021)]{cohen2021eos}
|
|
|
-Cohen et al. (2021). Gradient descent at the edge of stability. \textit{ICLR 2022}.
|
|
|
-\bibitem[Damian et al.(2023)]{damian2023selfstab}
|
|
|
-Damian et al. (2023). Self-stabilization. \textit{ICLR 2023}.
|
|
|
-\bibitem[Damian et al.(2022)]{damian2022neural}
|
|
|
-Damian et al. (2022). Neural networks can learn representations. \textit{COLT 2022}.
|
|
|
-\bibitem[Dohare et al.(2024)]{dohare2024plasticity}
|
|
|
-Dohare et al. (2024). Loss of plasticity in deep continual learning. \textit{Nature} 632:768--774.
|
|
|
-\bibitem[Foret et al.(2021)]{foret2021sam}
|
|
|
-Foret et al. (2021). Sharpness-aware minimization for generalization. \textit{ICLR 2022}.
|
|
|
-\bibitem[Ghorbani et al.(2019)]{ghorbani2019spectral}
|
|
|
-Ghorbani et al. (2019). An investigation into neural net optimization via Hessian eigenvalue density. \textit{ICML 2019}.
|
|
|
-\bibitem[Hu et al.(2021)]{hu2021lora}
|
|
|
-Hu et al. (2021). LoRA: Low-rank adaptation of large language models. \textit{ICLR 2022}.
|
|
|
-\bibitem[Liu et al.(2022)]{liu2022omnigrok}
|
|
|
-Liu et al. (2022). Omnigrok: Grokking beyond algorithmic data. \textit{ICLR 2023}.
|
|
|
-\bibitem[Lyle et al.(2023)]{lyle2023plasticity}
|
|
|
-Lyle et al. (2023). Understanding plasticity in neural networks. \textit{ICML 2023}.
|
|
|
-\bibitem[Nanda et al.(2023)]{nanda2023progress}
|
|
|
-Nanda et al. (2023). Progress measures for grokking via mechanistic interpretability. \textit{ICLR 2023}.
|
|
|
-\bibitem[Nikishin et al.(2022)]{nikishin2022primacy}
|
|
|
-Nikishin et al. (2022). The primacy bias in deep reinforcement learning. \textit{ICML 2022}.
|
|
|
-\bibitem[Papyan et al.(2020)]{papyan2020prevalence}
|
|
|
-Papyan et al. (2020). Prevalence of neural collapse during the terminal phase of deep learning training. \textit{PNAS}.
|
|
|
-\bibitem[Power et al.(2022)]{power2022grokking}
|
|
|
-Power et al. (2022). Grokking: Generalization beyond overfitting on small algorithmic datasets. \textit{arXiv:2201.02177}.
|
|
|
-\bibitem[Sagun et al.(2017)]{sagun2017empirical}
|
|
|
-Sagun et al. (2017). Empirical analysis of the Hessian of over-parametrized neural networks. \textit{arXiv:1706.04454}.
|
|
|
-\bibitem[Tishby and Schwartz-Ziv(2015)]{tishby2015deep}
|
|
|
-Tishby, N. and Schwartz-Ziv, R. (2015). Deep learning and the information bottleneck principle. \textit{ITW}.
|
|
|
-\bibitem[Yang and Hu(2021)]{yang2021feature}
|
|
|
-Yang, G. and Hu, E. (2021). Tensor programs IV: Feature learning in infinite-width neural networks. \textit{ICML 2021}.
|
|
|
-\bibitem[Zhao et al.(2023)]{zhao2023lowrank}
|
|
|
-Zhao et al. (2023). GaLore: Memory-efficient LLM training by gradient low-rank projection. \textit{ICML 2024}.
|
|
|
-\bibitem[Zhu et al.(2021)]{zhu2021geometric}
|
|
|
-Zhu et al. (2021). A geometric analysis of neural collapse with unconstrained features. \textit{NeurIPS 2021}.
|
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-\end{thebibliography}
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-
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-\appendix
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-\section{Proof Details}\label{app:proofs}
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-
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-\subsection*{Proof of Proposition~\ref{prop:e1e2}}
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-At $\tLF$: $\|\bR\|_2\leq CM\epsilon$. Signal term rank $\leq C-1$.
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-Davis-Kahan + (A1): $\gamma_C(\bJ^\top\bK\bJ)\geq\Omega(\rho-1)$.
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-Weyl: $\gamma_C(\bH)\geq\Omega(\rho-1)-2CM\epsilon>\delta_{\mathrm{gap}}$
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-for $\epsilon<(\rho-1)/(4CM)$. $\square$
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-
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-\subsection*{Proof of Proposition~\ref{prop:e2e3}}
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-Let $g_\perp=(I-\proj_k)\nabla\cL$. Since $\bH g_\|$ lies in top-$k$ subspace:
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-$\frac{d}{dt}\|g_\perp\|^2\leq-2\delta_{\mathrm{gap}}\|g_\perp\|^2$.
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-Gronwall: $\|g_\perp(t)\|\leq\|g_\perp(\tSE)\|e^{-\delta_{\mathrm{gap}}(t-\tSE)}$. $\square$
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-
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-\subsection*{Proof of Proposition~\ref{prop:e3e4}}
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-In E3 regime, $\Delta\btheta\approx-\eta\proj_k\nabla\cL$.
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-Covariance-tracking yields $\dot\psi\geq\mu(1-\psi)$,
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-$\mu=\eta\lambda_{\min}^+(\bG)/k$.
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-Integrating: $1-\psi(t)\leq(1-\psi_0)e^{-\mu(t-\tCSC)}$. $\square$
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-
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-\section{Relation to Information Bottleneck}\label{app:ib}
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-
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-The IB theory~\citep{tishby2015deep} proposes a two-phase model:
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-a fitting phase ($I(T;Y)$ grows) followed by a compression phase
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-($I(T;X)$ decreases). Our event framework provides a geometric
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-interpretation of each phase:
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-\begin{itemize}[leftmargin=1.2em,topsep=2pt,itemsep=1pt]
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- \item \emph{Fitting phase} $\equiv$ E1--E2: loss drops below $\epsilon_{\mathrm{LF}}$,
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- gradient mass concentrates, spectral edge forms.
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- \item \emph{Compression phase} $\equiv$ E3--E4: updates confined to top-$k$
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- block ($I(T;X)$ reducing); curvature rotates toward class-discriminative
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- directions ($I(T;Y)$ maintained).
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- \item \emph{Generalization} $\equiv$ E5: compression completes,
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- test accuracy jumps or NC geometry achieved.
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-\end{itemize}
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-The event language gives \emph{precise spectral conditions} for when each
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-IB phase begins and ends---resolving the operational ambiguity in the
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-original IB account.
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-
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-\section{Experimental Details}\label{app:exp-details}
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-
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-\subsection*{Exp-1 and Exp-3: Synthetic 5-class Setup}
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-All synthetic experiments use Gaussian clusters:
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-$n{=}400$ samples, $d{=}20$, $C{=}5$ classes,
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-cluster separation $\sigma_{\text{center}}{=}2.0$, within-cluster noise $0.8$.
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-Model: 3-layer MLP $[20{\to}64{\to}64{\to}5]$, ReLU activations.
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-Optimizer: SGD, $\eta{=}0.05$, no weight decay.
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-E2 detection: spectral gap proxy (max gradient norm / mean gradient norm
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-over $k{=}15$ random samples, threshold $1.4$).
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-Alignment regularizer (Exp-3): after E2 fires,
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-$\mathcal{L}_{\mathrm{align}} = \lambda \cdot \hat{g}_{\mathrm{top}}^\top \Delta\btheta / \|\Delta\btheta\|$
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-where $\hat{g}_{\mathrm{top}}$ is the unit vector of the highest-norm per-sample gradient.
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-
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-\subsection*{Exp-2: Grokking Setup}
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-Modular arithmetic ($a{+}b \bmod 23$),
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-529 total pairs, 50\% train split.
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-Model: embedding dim $d{=}16$, hidden $h{=}64$, 3-layer MLP.
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-Optimizer: AdamW, $\eta{=}5{\times}10^{-3}$, weight decay $\in\{0.01, 1.0\}$.
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-Spectral gap measured via gradient SVD every 8 epochs.
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-
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-\subsection*{Exp-4: Continual Learning Setup}
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-Controlled overlap: Task-B centers $= \alpha c_A + (1{-}\alpha)c_A^\perp$
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-for $\alpha\in\{0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0\}$ (3 seeds each, 21 trials).
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-Input dim $d{=}24$, $C{=}4$ classes, center scale $3.0$.
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-Model: backbone $[24{\to}64{\to}64]$ (Tanh) $+$ linear head.
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-Training: SGD $\eta{=}0.05$, momentum $0.9$, weight decay $10^{-3}$,
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-60 epochs per task. No replay.
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-PSim$(G_A, G_B)$: top-5 singular subspace alignment of
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-$8{\times}16$-sample gradient matrices.
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-
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-\subsection*{Reproducibility}
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-All experiments implemented in NumPy/PyTorch with fixed random seeds.
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-Code available at \texttt{workspace/run\_20260520\_*/code/}.
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-Runtime: Exp-1/3/5 $<$2 min (CPU), Exp-2 $\approx$3 min (CPU),
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-Exp-4 $\approx$90 s (CPU, 21 trials).
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-
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-\end{document}
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