\documentclass[aspectratio=169,dvipsnames]{beamer} \setbeamerfont{title}{family=\bf} \setbeamerfont{frametitle}{family=\bf} \setbeamerfont{normal text}{family=\rm} \setbeamertemplate{navigation symbols}{} \setbeamercolor{titlelike}{parent=structure,fg=cyan} \usepackage{enumitem} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} \usepackage{pifont} \usepackage{graphicx} \usepackage{xcolor} \usepackage{tikz} \definecolor{ictpblue}{HTML}{0471b9} \definecolor{ictpgreen}{HTML}{0c8636} \definecolor{mb}{HTML}{5e81b5} \definecolor{my}{HTML}{e19c24} \definecolor{mg}{HTML}{8fb032} \definecolor{mr}{HTML}{eb6235} \setbeamercolor{titlelike}{parent=structure,fg=ictpblue} \setbeamercolor{itemize item}{fg=ictpblue} \usepackage[ style=phys, eprint=true, maxnames = 100, terseinits=true ]{biblatex} \addbibresource{zif.bib} \title{ Understanding the flat parts of random landscapes } \author{\textbf{Jaron Kent-Dobias}} \date{9 September 2025} \begin{document} \begin{frame} \maketitle \vspace{-8pc} \begin{minipage}[c]{10pc} \centering \includegraphics[height=6pc]{figs/ift-unesp.png} \vspace{2em} \includegraphics[height=1.5pc]{figs/Simons-Foundation-Logo_blue.png} \end{minipage} \hfill\begin{minipage}[c]{10pc} \centering \includegraphics[height=6pc]{figs/logo-ictp-saifr.jpg} \vspace{2em} \includegraphics[height=1.5pc]{figs/fapesp.png} \end{minipage} \vspace{2pc} \end{frame} \begin{frame} \frametitle{How to count: Kac--Rice} Number of stationary points with $\nabla H(\pmb x)=0$ given by integral over Kac--Rice measure \begin{align*} \#_\text{points} &=\int_\Omega d\pmb x\,\delta\big(\nabla H(\pmb x)\big)\,\big|\det\operatorname{Hess}H(\pmb x)\big| \end{align*} Note absolute value of the determinant: want to account for curvature but not add $-1$ \bigskip Can specify properties of points by inserting $\delta$-functions: \begin{align*} \#_\text{points}\alert<2>{(E)} &=\int_\Omega d\pmb x\,\delta\big(\nabla H(\pmb x)\big)\,\big|\det\operatorname{Hess}H(\pmb x)\big| \alert<2>{\,\delta\big(H(\pmb x)-NE\big)} \end{align*} \emph{How do we condition on marginal minima?} \end{frame} \begin{frame} \frametitle{Conditioning on the type of minimum: the spherical models} \begin{columns} \begin{column}{0.5\textwidth} In spherical spin glasses, all points have the same Hessian spectral density: semicircle with radius $\mu_\text m$, but different shifts \[ \mu=\frac1N\operatorname{Tr}\operatorname{Hess} H(\pmb x) \] \bigskip Condition on marginal minima by inserting \[ \delta\big(\operatorname{Tr}\operatorname{Hess}H(\pmb x)-N\mu_\text{m}\big) \] \end{column} \begin{column}{0.5\textwidth} \begin{overlayarea}{\textwidth}{14.5em} \only<1-2>{\includegraphics[width=\columnwidth]{figs/mu_0.75.pdf}\\\hphantom{ello}\includegraphics[width=0.8\columnwidth]{figs/land_0.75.pdf}} \only<3>{\includegraphics[width=\columnwidth]{figs/mu_1.5.pdf}\\\hphantom{ello}\includegraphics[width=0.8\columnwidth]{figs/land_1.5.pdf}} \only<4>{\includegraphics[width=\columnwidth]{figs/mu_2.25.pdf}\\\hphantom{ello}\includegraphics[width=0.8\columnwidth]{figs/land_2.25.pdf}} \only<5>{\includegraphics[width=\columnwidth]{figs/mu_3.5.pdf}\\\hphantom{ello}\includegraphics[width=0.8\columnwidth]{figs/land_3.5.pdf}} \only<6>{\includegraphics[width=\columnwidth]{figs/mu_2.pdf}\\\hphantom{ello}\includegraphics[width=0.8\columnwidth]{figs/land_2.pdf}} \end{overlayarea} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{Less simple mean-field models} \framesubtitle{The mixed spherical spin glasses} \begin{columns} \begin{column}{0.41\textwidth} \alert<1-2>{Pure: all procedures reach $E_\text{th}$} \medskip \alert<3-4>{Mixed: different procedures reach different energies} \medskip Dynamical endpoints bounded by complexity of marginal minima \bigskip \tiny \fullcite{Folena_2020_Rethinking} \smallskip \fullcite{Folena_2021_Gradient} \smallskip \fullcite{Kent-Dobias_2023_How} \end{column} \begin{column}{0.59\textwidth} \begin{overlayarea}{\columnwidth}{0.8\textheight} \only<1>{% \includegraphics[width=0.8\columnwidth]{figs/complexity_3_marginal.pdf} }% \only<2>{% \bigskip \begin{minipage}[b]{0.83\columnwidth} \centering \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.25.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.25.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_3.5.pdf} \end{minipage} \raisebox{0.75em}{\includegraphics[width=0.15\columnwidth]{figs/energy_arrow.pdf}} } \only<3>{% \includegraphics[width=0.8\columnwidth]{figs/complexity_34_marginal.pdf} }% \only<4>{% \bigskip \begin{minipage}[b]{0.83\columnwidth} \centering \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_0.75.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_1.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.25.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.25.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_3.5.pdf} \includegraphics[width=0.18\columnwidth]{figs/land_2.25.pdf} \end{minipage} \raisebox{0.75em}{\includegraphics[width=0.15\columnwidth]{figs/energy_arrow_o1.pdf}} }% \end{overlayarea} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{Marginal minima in generic models} \begin{columns} \begin{column}{0.5\textwidth} \alert<1>{In spherical spin glasses, all points have the same Hessian spectral density: semicircle with radius $\mu_\text m$, but different shifts} \bigskip In generic models, spectral density depends on stationarity, energy, etc! \bigskip \alert<2>{Example: multi-spherical model \[ H(\{\boldsymbol s_1,\boldsymbol s_2\}) =H_p^{(1)}(\boldsymbol s_1)+H_p^{(2)}(\boldsymbol s_2)+\epsilon\boldsymbol s_1\cdot\boldsymbol s_2 \]} \hspace{-0.25em}In most models we don't understand the Hessian at all \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1>\includegraphics[width=\columnwidth]{figs/mu_0.75.pdf} \onslide<2>\includegraphics[width=0.9\columnwidth]{figs/msg_marg_spectra.pdf} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{Towards generic marginal complexity} \begin{columns} \begin{column}{0.6\textwidth} \begin{itemize}[leftmargin=4em] \item[\color{ictpgreen}\bf Trick \#1:] condition stationary points on \emph{value of smallest eigenvalue} \end{itemize} { \small \begin{align*} \hspace{-1em}&\delta(\lambda_\text{min}(A)) \\ &=\lim_{\beta\to\infty}\int \frac{d\pmb s\,\delta(N-\|\pmb s\|^2)e^{-\beta\pmb s^TA\pmb s}} {\int d\pmb s'\,\delta(N-\|\pmb s'\|^2)e^{-\beta\pmb s'^TA\pmb s'}} \delta\left(\frac{\pmb s^TA\pmb s}N\right) \end{align*} } \bigskip Only works if you happen to have the correct shift $\mu$ \bigskip \tiny \fullcite{Kent-Dobias_2024_Conditioning} \end{column} \begin{column}{0.4\textwidth} \begin{overprint} \onslide<1>\includegraphics[width=\textwidth]{figs/spectrum_less.pdf} \onslide<2>\includegraphics[width=\textwidth]{figs/spectrum_more.pdf} \onslide<3>\includegraphics[width=\textwidth]{figs/spectrum_eq.pdf} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{Towards generic marginal complexity} \begin{columns} \begin{column}{0.5\textwidth} \begin{itemize}[leftmargin=4em] \item[\color{ictpgreen}\bf Trick \#1:] condition stationary points on \emph{value of smallest eigenvalue} \end{itemize} { \small \begin{align*} \hspace{-3em}&\delta(\lambda_\text{min}(A)) \\ \hspace{-3em}&=\lim_{\beta\to\infty}\int \frac{d\pmb s\,\delta(N-\|\pmb s\|^2)e^{-\beta\pmb s^TA\pmb s}} {\int d\pmb s'\,\delta(N-\|\pmb s'\|^2)e^{-\beta\pmb s'^TA\pmb s'}} \delta\left(\frac{\pmb s^TA\pmb s}N\right) \end{align*} } \medskip \begin{itemize}[leftmargin=4em] \item[\color{ictpgreen}\bf Trick \#2:] adjust $\mu\propto\operatorname{Tr}\operatorname{Hess}H$ until order-$N$ large deviation breaks \end{itemize} \bigskip \tiny \fullcite{Kent-Dobias_2024_Conditioning} \end{column} \begin{column}{0.5\textwidth} \hspace{0.9em} \includegraphics[scale=0.8]{figs/spectrum_less.pdf} \hspace{-1.6em} \includegraphics[scale=0.8]{figs/spectrum_eq.pdf} \hspace{-1.6em} \includegraphics[scale=0.8]{figs/spectrum_more.pdf} \\ \includegraphics[scale=0.8]{figs/large_deviation.pdf} \vspace{-1em} \small \begin{align*} \hspace{-0.5em}G_0(\mu)=\frac 1N\log\Big\langle\delta\big(\lambda_\text{min}(A-\lambda\mu)\big)\Big\rangle_{A\in\text{GOE}(N)} \end{align*} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{Marginal complexity: example} \begin{columns} \begin{column}{0.5\textwidth} Example: model of nonlinear least squares: \[ H(\pmb s)=\frac12\sum_{i=1}^{M}V_i(\pmb s)^2 \] for spherical $\pmb s\in\mathbb R^N$ and $M=\alpha N$ inhomogeneous random functions $V_i$ \[ V_i(\boldsymbol s)=H_2^{(i)}(\boldsymbol s)+H_3^{(i)}(\boldsymbol s) \] \bigskip \tiny \fullcite{Kent-Dobias_2024_Conditioning} \smallskip \fullcite{Kent-Dobias_2024_Algorithm-independent} \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1>\vspace{4em}\includegraphics[width=\textwidth]{figs/most_squares_complex.pdf} \onslide<2>\vspace{-1.75em}\includegraphics[width=\textwidth]{figs/most_squares_complexity.pdf} \vspace{-1.95em} \hspace{-0.25em}\colorbox{white}{\includegraphics[width=\textwidth]{figs/most_squares_stability.pdf}} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{The Euler characteristic \boldmath{$\chi$}} \begin{columns} \begin{column}{0.5\textwidth} The Euler characteristic $\chi(\Omega)$ is a topological invariant of a manifold $\Omega$ \medskip Defined by tiling the manifold, then taking the alternating sum \begin{align*} \chi(\Omega_{\text{cow}}) &= {\only<2,5->{\color{Red}}\#_\text{vertices}} &&\hspace{-1em}- {\only<3,5->{\color{ictpgreen}}\#_\text{edges}} &&\hspace{-1em}+ {\only<4,5->{\color{ictpblue}}\#_\text{faces}} \\ &\color{White}\only<2->{\color{Black}}= {\only<2,5->{\color{Red}}2904} &&\hspace{-1em}\color{White}\only<3->{\color{Black}}- {\only<3,5->{\color{ictpgreen}}8706} &&\hspace{-1em}\color{White}\only<4->{\color{Black}}+ {\only<4,5->{\color{ictpblue}}5804} \\ &\color{White}\only<5->{\color{Black}}=2 \end{align*} \[ \color{White}\only<6->{\color{Black}}\chi(\Omega_\text{football}) ={\only<6->{\color{Red}}60}-{\only<6->{\color{ictpgreen}}90}+{\only<6->{\color{ictpblue}}32}=2 \] \color{White}\only<7>{\color{Black}}Cow is homeomorphic to a sphere \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1,5>\includegraphics[width=\textwidth]{figs/cow.png} \onslide<2>\includegraphics[width=\textwidth]{figs/cow_vert.png} \onslide<3>\includegraphics[width=\textwidth]{figs/cow_edge.png} \onslide<4>\includegraphics[width=\textwidth]{figs/cow_face.png} \onslide<6->\hspace{2em}\includegraphics{figs/Football_Pallo_valmiina-cropped.jpg} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{The Euler characteristic \boldmath{$\chi$}} \framesubtitle{Characteristics of the characteristic} \begin{columns} \begin{column}{0.5\textwidth} For closed, connected 2-dimensional manifolds, related to genus $g$ by $\chi=2-2g$ \medskip General properties: \vspace{-0.5em} \[ \chi(\Omega)=0 \text{ for odd-dimensional $\Omega$} \] \vspace{-1.6em} \[ \chi(S^D)=2\text{ for even }D \] \[ \chi(\Omega_1\sqcup\Omega_2)=\chi(\Omega_1)+\chi(\Omega_2) \] \[ \chi(\Omega_1\times\Omega_2)=\chi(\Omega_1)\times\chi(\Omega_2) \] \smallskip Examples: \vspace{-0.5em} \[\chi(M\text{ even-$D$ spheres})=2M\] \vspace{-1.6em} \[\chi(S^1\times\text{anything})=0\] \end{column} \begin{column}{0.5\textwidth} \includegraphics[width=\textwidth]{figs/genus.png} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{The Euler characteristic \boldmath{$\chi$}} \framesubtitle{Computing the Euler characteristic} \begin{columns} \begin{column}{0.5\textwidth} Morse theory: gradient flow on an arbitrary ``height'' function $h$ makes a complex \begin{align*} \chi(\Omega) &= {\only<2,5>{\color{Red}}\#_\text{vertices}} - {\only<3,5>{\color{ictpgreen}}\#_\text{edges}} + {\only<4,5>{\color{ictpblue}}\#_\text{faces}} +\cdots \\ &= {\only<6>{\color{ictpblue}}\#_\text{index 0}} - {\only<6>{\color{ictpgreen}}\#_\text{index 1}} + {\only<6>{\color{Red}}\#_\text{index 2}} +\cdots \\ &=\sum_{i=0}^D(-1)^i\#_\text{index i} \end{align*} \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1>\includegraphics[width=\textwidth]{figs/other_sphere.png} \onslide<2>\includegraphics[width=\textwidth]{figs/other_sphere_vert.png} \onslide<3>\includegraphics[width=\textwidth]{figs/other_sphere_edge.png} \onslide<4>\includegraphics[width=\textwidth]{figs/other_sphere_face.png} \onslide<5>\includegraphics[width=\textwidth]{figs/other_sphere_all.png} \onslide<6>\includegraphics[width=\textwidth]{figs/other_sphere_crit.png} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{The Euler characteristic \boldmath{$\chi$}} \framesubtitle{Computing the Euler characteristic} \begin{columns} \begin{column}{0.6\textwidth} \[ \Omega=\left\{ \pmb a\in\mathbb R^N\mid\|\pmb a\|^2=N, V_0=\hat f(J^i\mid\pmb a)\;\forall\;1\leq i\leq M \right\} \] Pick whatever height function $h:\Omega\to\mathbb R$ you like: $h(\pmb a)=\frac1N\pmb a_0\cdot\pmb a$ for arbitrary $\pmb a_0$ \[ \#_{\substack{\text{critical}\\\text{points}}} =\int_\Omega d\pmb x\, \delta\big(\nabla h(\pmb x)\big)\, \big|\det\operatorname{Hess}h(\pmb x)\big| \] \[ \hspace{-1em}\operatorname{sgn}\big(\det\operatorname{Hess}(\pmb x)\big) = \operatorname{sgn}\left(\prod_{i=1}^D\lambda_i\right) =(-1)^{\text{index}} \] \[ \chi(\Omega) =\sum_{i=0}^D(-1)^i\#_\text{index i} =\int_\Omega d\pmb x\,\delta\big(\nabla h(\pmb x)\big)\,\det\operatorname{Hess}h(\pmb x) \] \end{column} \begin{column}{0.4\textwidth} \begin{overprint} \onslide<1>\includegraphics[width=\textwidth]{figs/function_1.png} \onslide<2>\includegraphics[width=\textwidth]{figs/function_2.png} \onslide<3>\includegraphics[width=\textwidth]{figs/function_3.png} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{A simple model of nonlinear least squares} \framesubtitle{Results} \begin{columns} \begin{column}{0.5\textwidth} $M$ data points, $N$ parameters, $\alpha=M/N$ \[ V_0=\hat f(J\mid \pmb a) =\sum_{i_1=1}^N\cdots\sum_{i_p=1}^NJ_{i_1,\ldots,i_p}a_{i_1}\cdots a_{i_p} \] Simplest case: $p=1$, $\Omega$ is intersection of random hyperplanes with the sphere \medskip Results in $\chi(\Omega)=2$ or $\chi(\Omega)=0$ depending on whether solutions exist \medskip \hspace{2em}\includegraphics[width=0.33\textwidth]{figs/connected.pdf} \hfill \includegraphics[width=0.33\textwidth]{figs/gone.pdf}\hspace{2em} \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1>\includegraphics[width=\textwidth]{figs/intersections_1.pdf} \onslide<2>\includegraphics[width=\textwidth]{figs/intersections_2.pdf} \onslide<3>\includegraphics[width=\textwidth]{figs/intersections_3.pdf} \onslide<4>\includegraphics[width=\textwidth]{figs/intersections_4.pdf} \onslide<5>\includegraphics[width=\textwidth]{figs/phases_1.pdf} \end{overprint} \end{column} \end{columns} \end{frame} \begin{frame} \frametitle{A simple model of nonlinear least squares} \framesubtitle{Results} \begin{columns} \begin{column}{0.5\textwidth} $M$ data points, $N$ parameters, $\alpha=M/N$ \[ V_0=\hat f(J\mid \pmb a) =\sum_{i_1=1}^N\cdots\sum_{i_p=1}^NJ_{i_1,\ldots,i_p}a_{i_1}\cdots a_{i_p} \] For $p\geq2$, different phases with $|\chi(\Omega)|\gg1$ with varying sign \medskip \includegraphics[width=0.23\textwidth]{figs/middle.pdf} \includegraphics[width=0.23\textwidth]{figs/complex.pdf} \includegraphics[width=0.23\textwidth]{figs/shattered.pdf} \includegraphics[width=0.23\textwidth]{figs/gone.pdf} \end{column} \begin{column}{0.5\textwidth} \begin{overprint} \onslide<1>\centering\includegraphics[width=0.8\textwidth]{figs/middle.pdf}\\$\chi(\Omega)\ll0$ \onslide<2>\centering\includegraphics[width=0.8\textwidth]{figs/complex.pdf}\\$\chi(\Omega)\ll0$ \onslide<3>\centering\includegraphics[width=0.8\textwidth]{figs/shattered.pdf}\\$\chi(\Omega)\gg0$ \onslide<4>\includegraphics[width=\textwidth]{figs/phases_2.pdf} \onslide<5>\includegraphics[width=\textwidth]{figs/phases_3.pdf} \onslide<6>\includegraphics[width=\textwidth]{figs/phases_4.pdf} \end{overprint} \end{column} \end{columns} \end{frame} \end{document}