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4 papers in cond-mat.dis-nn
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cs.LGcond-mat.dis-nnstat.ML Haotian Gu, Yizhou Xu, Lenka Zdeborov\'a · Oct 1, 2026

This paper studies nonlinear in-context learning via single-index models, comparing a kernel learner (fixed spherical-harmonic features followed by linear attention) against a feature learner (linear attention on raw inputs followed by a learned nonlinear readout). Using the replica method, the authors derive predictions for memorization and generalization errors across varying pretraining data, task diversity, and context lengths, and validate them numerically over a broad parameter range. The analysis reveals phase diagrams for architectural advantage and qualitatively different context-length scalings: the kernel learner needs $L = \Theta(d^k)$ to recover degree-$k$ harmonics, while the feature learner exploits all teacher components at $L = \Theta(d)$.

In-context learning (ICL) enables a pretrained model to infer a task from demonstrations without updating its parameters. While much of the existing theory focuses on linear target functions, in this paper we study nonlinear cases by comparing two one-layer attention architectures on the same family of single-index tasks. A kernel learner first maps inputs through a fixed nonlinear feature map and then applies linear attention, whereas a feature learner applies attention to the original input, followed by a learned nonlinear readout. We derive predictions for their memorization and generalization errors using the replica method, retaining the effects of pretraining size, task-pool diversity, and training and inference context lengths. The resulting predictions closely match numerical experiments across a broad range of regimes. Our analysis yields phase diagrams that characterize when each architecture is advantageous as the amount of pretraining data, task diversity, and context lengths vary. We further identify qualitatively different context-length scalings for the two learners. Together, these results clarify how architectural choices interact with the dataset and govern nonlinear in-context learning.
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stat.MLcond-mat.dis-nncs.LG Jorge Medina Moreira, Lorenzo Bardone, Lenka Zdeborov\'a · Oct 1, 2026

This paper develops a high-dimensional theory for why masked autoencoders learn better representations than standard autoencoders. In a spiked model with heterogeneous noise, the authors prove that a linear masked autoencoder recovers the latent feature at linear sample complexity $n=O(d)$ where PCA fails. They further quantify how dynamic mask resampling lowers sample complexity compared to static masking, and validate the qualitative predictions in CNNs, vision transformers, and a BERT pilot.

Why can masked prediction learn useful representations that unmasked reconstruction misses? We study this question in a high-dimensional model of a masked autoencoder (MAE) trained on data with shared latent structure and heterogeneous noise. We prove that masked linear reconstruction can recover the latent feature at linear sample complexity in regimes where unmasked linear reconstruction, equivalent to PCA, fails. The analysis also quantifies the statistical advantage of mask resampling, an established ingredient of masked pretraining. By introducing a fixed collection of $K$ masks per sample, we characterize its effect on feature recovery and downstream performance, identifying regimes where greater mask diversity lowers sample complexity. Guided by this prediction, we find that random cropping and flipping in standard image-training pipelines can obscure the advantage of mask resampling by renewing the prediction task even when the patch mask is fixed. Removing these transformations reveals a downstream advantage for dynamic over static masking in CNN autoencoders and vision transformers. A complementary BERT pilot finds benefits from greater mask diversity on downstream language tasks. Our results separate the benefit of the masked prediction objective from that of mask diversity, and show how a tractable theory can guide experiments that uncover advantages hidden by standard training practices.
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cs.LGcond-mat.dis-nn Qiuliang Liu, Liming Wu, Qi Li et al. · Oct 1, 2026

Disorder is ubiquitous in functional crystals—nearly half of ICSD entries show some form of disorder—yet most generative models assume perfectly ordered lattices with deterministic site occupations. EP-Flow attacks formula-conditioned disordered crystal structure prediction without site-level annotations by representing occupancies as an Occupancy Distribution Matrix (ODM) that lives on a formula-dependent transportation polytope. It proposes a flow-matching model that canonicalizes heterogeneous polytopes into a shared double-centered space via log-domain double centering, learns a marginal-preserving velocity field, and recovers valid occupancies with a differentiable Sinkhorn inverse map, jointly generating fractional coordinates and lattice parameters. If the absolute performance can be scaled, this formalism could become a standard way to handle substitutional, vacancy, and interstitial disorder in generative materials design.

Generative models have made rapid progress in ordered crystal structure prediction, yet many functional materials are intrinsically disordered, with substitutional mixing, vacancies, or interstitial species controlling their properties. Existing crystal generators either assume deterministic site occupations or require site-level disorder annotations, which are often unavailable when the chemical formula is the primary input. We formulate disordered crystal structure prediction through an Occupancy Distribution Matrix (ODM), a continuous site-by-species representation that unifies ordered crystals, solid solutions, vacancy disorder, and interstitial occupancy. A valid ODM must satisfy coupled site-wise occupancy, mass-conservation, and non-negativity constraints, placing each sample on a formula-dependent transportation polytope. We propose Entropic Polytope Flow (EP-Flow), a marginal-constrained flow matching framework that canonicalizes heterogeneous polytopes into a shared double-centered space, learns a marginal-preserving flow, and recovers feasible occupancies through a Sinkhorn inverse map. By jointly generating occupancies, fractional coordinates, and lattice parameters, EP-Flow achieves state-of-the-art performance on formula-conditioned disordered CSP benchmarks derived from COD and MPDS, substantially outperforming adapted ordered-crystal generators. Analyses further show that EP-Flow recovers sparse and chemically meaningful local disorder patterns rather than merely matching global composition statistics.
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cs.LGcond-mat.dis-nncond-mat.stat-mech Emil Albrychiewicz, Andr\'es Franco Valiente, Li-Ching Chen et al. · Mar 22, 2026

Recent theoretical models of diffusion as coupled Ornstein-Uhlenbeck processes predict a hierarchy of interaction timescales creating a synchronization gap between global and local committing modes. This work investigates how this gap mechanistically emerges within pretrained Diffusion Transformers by introducing a controlled architectural realization of replica coupling via symmetric cross-attention gates with strength $g$. Through linearized analysis and empirical probing of DiT-XL/2 across all 28 layers, the authors demonstrate that the gap is an intrinsic, depth-localized property that collapses under strong coupling as $\mathcal{O}(\frac{1-g}{1+g})$, providing a bridge between continuous statistical physics and discrete transformer dynamics.

Recent theoretical models of diffusion processes, conceptualized as coupled Ornstein-Uhlenbeck systems, predict a hierarchy of interaction timescales, and consequently, the existence of a synchronization gap between modes that commit at different stages of the reverse process. However, because these predictions rely on continuous time and analytically tractable score functions, it remains unclear how this phenomenology manifests in the deep, discrete architectures deployed in practice. In this work, we investigate how the synchronization gap is mechanistically realized within pretrained Diffusion Transformers (DiTs). We construct an explicit architectural realization of replica coupling by embedding two generative trajectories into a joint token sequence, modulated by a symmetric cross attention gate with variable coupling strength g. Through a linearized analysis of the attention difference, we show that the replica interaction decomposes mechanistically. We empirically validate our theoretical framework on a pretrained DiT-XL/2 model by tracking commitment and per layer internal mode energies. Our results reveal that: (1) the synchronization gap is an intrinsic architectural property of DiTs that persists even when external coupling is turned off; (2) as predicted by our spatial routing bounds, the gap completely collapses under strong coupling; (3) the gap is strictly depth localized, emerging sharply only within the final layers of the Transformer; and (4) global, low frequency structures consistently commit before local, high frequency details. Ultimately, our findings provide a mechanistic interpretation of how Diffusion Transformers resolve generative ambiguity, isolating speciation transitions to the terminal layers of the network.