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cs.LGnlin.CD Hiroto Tamura, Gouhei Tanaka · Oct 1, 2026

This paper addresses the challenge of learning minimal, interpretable piecewise-linear representations of unknown nonlinear dynamical systems from time-series data. The authors propose training a higher-capacity almost-linear RNN first, then hierarchically reducing it via a fixed-point-guided procedure that linearizes redundant ReLU units while preserving distinct fixed-point symbols, and finally retraining the compact model from the parent initialization. The central insight is that redundant nonlinear capacity can act as a structural and optimization scaffold for discovering reliable minimal models, which matters because directly training at the theoretical minimal capacity often fails catastrophically.

Understanding a nonlinear dynamical system from time series requires not only reproducing its trajectories, but also identifying a simple representation that preserves its essential dynamical structure. Almost-linear recurrent neural networks (AL-RNNs) are piecewise-linear RNNs in which only a subset of units use ReLU nonlinearities, so that nonlinear capacity is explicitly controlled by the number of ReLU units. Their activation patterns define linear regions, represented as symbols, whose observed transitions form a symbolic transition graph. However, directly training AL-RNNs with few ReLU units to realize minimal dynamical representations can be unreliable. We ask whether an AL-RNN with more ReLU units can instead be trained first and systematically reduced to a minimal dynamical representation. We introduce a fixed-point-guided hierarchical reduction procedure that progressively linearizes selected ReLU units, merging neighboring linear regions and graph nodes while preserving distinct symbols containing fixed points (FPs). The resulting reduction tree defines a hierarchy of progressively simpler candidates. Each reduced candidate is initialized from the parent parameters and retrained under guidance from the parent dynamics. We also prove that reproducing $Q$ distinct fixed points requires at least $Q$ FP-containing symbols, providing a certificate of symbol-level minimality when this bound is attained. On the 3-scroll Chua system, direct training with the theoretical minimum of three ReLU units achieves high-fidelity minimal realizations in only 20% of seeds, whereas our learn-reduce-retrain strategy increases the seed-macro success rate to approximately 71% at the same final nonlinear capacity. These results show that redundant nonlinear capacity can serve as a scaffold for discovering and realizing minimal dynamical representations.
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cs.LGstat.ML Kotaro Kamiya, Joel Nicholls · Oct 1, 2026

Kamiya and Nicholls introduce the Clifford Sheaf Neural Network (CSNN), a geometric-graph architecture that places Clifford-algebra stalks on cellular sheaves and transports multivector features with learned restriction maps. The core advance is replacing versor conjugation with a normalized reversion sandwich $s_c(x)=c x \tilde{c}/q(c)$, yielding a sheaf Laplacian that stays positive semidefinite by construction while mixing feature grades. Despite a careful theoretical map of the design space, the paper contains no empirical experiments, leaving its practical value for graph-level regression entirely unproven.

We introduce the Clifford Sheaf Neural Network (CSNN), an equivariant sheaf neural network for geometric graphs that places a Clifford algebra on each stalk of a cellular sheaf and transports multivector features along edges. The canonical choice of restriction map for sheaves with algebra-valued stalks is algebra homomorphism. Adding the constraint of equivariance, the naive choice becomes versor conjugation. However, versor conjugation is expressively weak, so we drop algebra homomorphism and arrive at the K-term sandwich. The resulting sheaf Laplacian is positive semidefinite by construction, needs no versor constraint, and still mixes grades. Our main contribution characterizes the resulting family of restriction maps along three axes: which grades a map couples, how much of the endomorphism space it reaches, and how well it is conditioned. The K-term sandwich spans half of the endomorphism space, and in Cl(3, 0, 0) it corresponds to the maps that commute with the central pseudoscalar. The number of terms controls expressivity. CSNN is the reversion member, a first-order model by construction and the grade-mixing corner of this family, developed as a sheaf construction for graph-level equivariant regression.
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cs.SIcs.LG Alexandra Dache, Manon Rustin, Arnaud Vandaele et al. · Oct 1, 2026

This paper tackles community detection in multilayer networks where connectivity patterns and node degrees vary across layers. The proposed method, mFROST, jointly factorizes each layer via orthogonal symmetric nonnegative matrix trifactorization $A_l \approx D_l V \theta_l (D_l V)^\top$, enforcing shared community assignments $V$ while allowing layer-specific degree corrections $D_l$ and community interactions $\theta_l$. This flexibility matters because real-world multiplex networks often exhibit heterogeneous node sociability and diverse block structures that simpler shared-factor models miss.

Multilayer networks allow the modeling of interactions between the same entities across different contexts, such as temporal observations, varying settings, or interactions of different types. The goal of community detection in multilayer networks is to identify groups of nodes exhibiting similar connectivity patterns, which may vary across layers. We propose a method based on a joint nonnegative symmetric matrix trifactorization for community detection in multilayer networks, where each graph is approximated by a nonnegative symmetric matrix trifactorization. Our approach enforces constraints on the factor matrices so that communities are disjoint and shared across layers, while allowing each layer to have its own connectivity patterns and node degrees. This flexibility enables the model to capture both local and global structural variations across layers. We also develop an algorithm to efficiently solve this problem. We evaluate multilayer community detection methods using the multilayer degree-corrected stochastic block model (MDCBM), a flexible framework for generating realistic multilayer graphs with heterogeneous degrees and varying connectivity patterns. Experiments show that our method reliably detects communities across diverse regimes, whereas existing state-of-the-art approaches are often limited by restrictive structural assumptions.
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cs.LGcs.AImath.ST Hanna Malet, Gabriel Turinici · Oct 1, 2026

This paper studies model collapse in diffusion models under a fixed-budget data regime, where synthetic data accumulates but each generation trains on a constant-size subsample from the growing pool. Unlike prior work on total replacement (rapid collapse) or unbounded accumulation (collapse avoided), the authors argue that fixed budgets yield partial, feature-selective collapse: "fragile" features with large eigenvalues in a linearized parameter dynamics model decay quickly, while "robust" features with small eigenvalues persist for exponentially many generations. They support this with theory (stochastic recursion giving per-feature halving times) and experiments on 2D spirals, MNIST, Fashion-MNIST, and CIFAR-10.

Model collapse arises when generative models are trained on synthetic data produced by earlier models. The phenomenon has attracted considerable attention because of its societal and technical implications. However, previous studies have reached seemingly contradictory conclusions: replacing real data with synthetic data causes collapse (Shumailov et al.), yet accumulating real data alongside synthetic data can prevent it. For diffusion models, we study an intermediate regime typical of finite-budget pipelines: all past datasets and the real data are kept, but each new model is trained on a fixed-size sample from this growing pool, so the real fraction vanishes without any data being removed. Experiments on a 2D spiral dataset as well as the image benchmarks (MNIST, Fashion-MNIST, and CIFAR-10) show that replacement protocol degrades dataset rapidly as in the literature, whereas the fixed budget degrades only partially, sparing some features. A linear-response model of the multi-generational parameter dynamics, analyzed by stochastic recursion, confirms that the two protocols differ: some features will be fragile and lost within a few generations for both protocols, while some will be robust and preserved over practically unbounded horizons under the fixed budget protocol.
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cs.LG Pascal Janetzky, Yuxin Wang, Michael Klar et al. · Oct 1, 2026

Neural architecture search is bottlenecked by the cost of obtaining ground-truth performance labels. ppNAS addresses this by fusing a small set of labeled architectures with a large set of zero-cost proxies via prediction-powered inference. The core insight is to construct pairwise ranking supervision from both sources and debias systematic discrepancies using a rectified PPI objective, yielding state-of-the-art results under tight evaluation budgets.

Evaluating candidate architectures in neural architecture search (NAS) faces an inherent trade-off: on the one hand, reliable performance labels are limited because training and evaluating architectures is costly; on the other hand, zero-cost proxies (ZCPs) are cheap to compute at large scale but can be noisy. Yet, how to effectively combine these two sources of supervision remains unclear. In this paper, we propose PPNAS, a novel prediction-powered inference (PPI) approach for NAS. PPNAS fuses (1) a small set of architectures with observed performance labels and (2) a large set of architectures with ZCP information. To combine these two sources of supervision, PPNAS exploits the ordinal information provided by ZCPs to construct additional pairwise ranking supervision, while PPI debiases systematic discrepancies between ZCP-based and true performance rankings. We evaluate PPNAS in end-to-end predictor-based NAS, where it achieves state-of-the-art under limited evaluation budgets. To the best of our knowledge, PPNAS is the first prediction-powered approach for label-efficient NAS.
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cs.LGcs.SYeess.SY Simon Heilig, Jens P\"uttschneider, Mohammad Itani et al. · Oct 1, 2026

Standard stable port-Hamiltonian neural networks (s-PHNNs) enforce a single global minimum in the learned Hamiltonian, limiting them to systems with exactly one attractor. The authors overcome this by parametrizing the Hamiltonian as a product of Bregman divergences generated by a single fully input-convex neural network (FICNN), yielding a model---the ms-PHNN---that can represent multiple asymptotically stable equilibria while retaining local stability certificates by construction. This matters because many physical systems, from buckled beams to magnetic pendulums, exhibit multi-stable energy landscapes that existing guaranteed-stable neural ODEs cannot capture.

Stable port-Hamiltonian neural networks certify asymptotic stability by construction. Yet, their Hamiltonian is a global Lyapunov function with a single global minimum, so they can represent only dynamic systems with {one} attractor. We demonstrate that this excludes even simple systems with energy landscapes forming a double well, and we overcome the restriction by parametrising the Hamiltonian as a {product} of Bregman divergences generated by one input-convex network. We prove that the resulting model is locally Lyapunov stable, that the coexistence of stable equilibria forces additional non-asymptotically-stable equilibria to exist, that all equilibria lie in a bounded region, and under a hyperbolicity assumption that almost-everywhere stability holds. On three systems our approach is able to recover the energy surface characteristics and improve the convergence speed by 1.8$\times$-8.5$\times$.
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cs.LG Jingyao Zhang, Yuxuan Li, Lu Han et al. · Oct 1, 2026

Standard variational information bottleneck (VIB) regularizes representations by penalizing a single global mutual information $I(Z;X)$, which inherently treats all encoded information as equally valuable. This paper identifies a structural limitation: under a label-induced partition $C=\pi(Y)$, the chain rule gives $I(Z;X)=I(Z;C)+I(Z;X\mid C)$, so scalar compression conflates condition-level structure with residual within-condition variation. The authors propose a dual-bottleneck objective combining a standard KL term for global capacity and a conditional KL term that targets within-condition information, instantiated with a simplex-structured conditional prior. The result is a principled regularizer that integrates into existing pipelines and shows the clearest empirical benefits in low-data classification and medical-image segmentation, exactly where nuisance-like residual variation can dominate.

Standard information bottleneck (IB) regularization constrains representations via a single scalar I(Z;X), implicitlytreating all information as homogeneous. However, a single global compression control couples label-relevant structurewith residual within-condition variation, rather than regulating their allocation independently, allowing nuisanceinformation to persist in learned representations. For example, in medical imaging applications, residual variation oftenstems from acquisition conditions, background factors, or subject-specific appearance. This issue becomes particularlypronounced in data-limited settings, where models tend to overfit such variation, hindering generalization. While existingregularization methods can stabilize training, control capacity, or shape representation geometry, they do not explicitlyseparate nuisance-like variation from task-supporting structure. To address this limitation, we revisit IB from a structuredperspective based on a label-induced partition, where condition-level structure and within-condition information playdistinct roles. This leads to a dual-bottleneck formulation: a standard KL term controls global information capacity, while aconditional KL term targets within-condition information. We show that the conditional KL admits an exact decompositioninto a within-condition information term and a prior-mismatch term, explaining its alignment with the design objective.With a simplex-structured conditional prior, the method provides controllable latent geometry and integrates seamlesslyinto existing pipelines. Experiments on classification and segmentation show the clearest gains in low-data classificationand consistent improvements across dense prediction benchmarks.
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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.LG Santiago Florido Gomez, St\'ephane Rivaud · Oct 1, 2026

Neural scaling laws favor ever-larger models, but deciding when a network actually needs more capacity remains ad hoc. CAGE-NAS proposes a theoretically grounded rule: keep the architecture fixed only while the current parameter space can certify a valid functional gradient descent step; otherwise, expand the structure in a function-preserving way. By coupling growth decisions to the geometry of the empirical tangent space, the method unifies training and architecture adaptation under a single convergence certificate. On a controlled synthetic regression task, it discovers compact three-layer MLPs that sit in the extreme top tail of an exhaustive post-hoc search, though the evaluation remains limited to a toy benchmark.

The progressive growth of neural networks requires deciding when the current representation remains sufficient for optimization and when it should be expanded. CAGE-NAS formulates this decision in function space through an admissibility criterion on approximations of the functional gradient. As long as a representation enables a certified Functional Gradient Descent step, the architecture remains fixed; when the criterion fails, a function-preserving expansion is applied and the resulting representation is evaluated again. As the main instance, we study the family induced by the tangent space, using a regularized projection of the functional gradient. In a controlled setting with exact certification, CAGE-NAS produces architectures positioned above the 99.8th performance percentile by held-out RMSE among all admissible alternatives within the same parameter budget, without enumerating them during the growth trajectory.
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cs.ROcs.LG Giulio Schiavi, Andrei Cramariuc, Michael Pantic et al. · Oct 1, 2026

Standard grasp synthesis systems freeze their parameters after offline training and struggle with unfamiliar objects. This paper presents a continual-learning framework that replaces the fixed parametric scorer with a memory-based non-parametric model in a learned embedding space, augmented by recalling and transferring user demonstrations to new scenes via geometric registration. Instead of gradient-based finetuning, the robot adapts by adding grasp outcomes and demonstrations to structured memories, which enables fast, lightweight updates during real-world deployment with limited forgetting.

Most current grasp synthesis systems are trained offline and remain fixed during deployment. While this works well when deployment conditions resemble the training data, performance can degrade when robots encounter conditions they have not seen before, such as unfamiliar objects. In this work, we present a continual-learning framework for single-view 6-DoF grasp synthesis for a parallel-jaw gripper in cluttered scenes. Rather than finetuning a large parametric model, our method adapts through memory in a learned embedding space: grasp outcomes update future grasp scores, while optional user demonstrations are recalled and transferred to new scenes as additional candidate grasps. We evaluate our method in simulation and in extensive real-world experiments comprising over 1500 grasp trials. We show that our method matches the performance of existing 6-DoF grasping baselines even before adaptation, improves online on unseen objects from categories absent or underrepresented during training, and supports long-horizon continual learning with limited forgetting. In real-world experiments, our method reaches over 90\% success rates on several challenging object categories after only 50 online grasp attempts. Videos and code at https://giuschio.github.io/cl_grasping/.
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cs.LGcs.AI Mehmet Baygin, Sengul Dogan, Turker Tuncer · Oct 1, 2026

This tutorial reframes model validation as the design of a performance estimator rather than a mere software setting. It surveys splits from hold-out to nested group cross-validation, links geometric fold choices to the correct independent unit (record, subject, center), and provides eight controlled leakage scenarios grounded in biomedical examples such as EEG epochs and paired-eye OCT. The core argument is that an elaborate fold structure is scientifically invalid if applied to the wrong unit, and that even a simple hold-out can be rigorous when the unit, size, and isolation constraints are correct.

Model validation estimates the performance of a complete learning procedure on new data. However, an invalid split can produce an optimistic and stable result. This tutorial reviews hold-out validation, train/validation/test designs, repeated random subsampling, k-fold and repeated stratified cross-validation, leave-one-out and leave-p-out schemes, group-aware validation, and nested group cross-validation. General machine-learning principles are linked to EEG epochs, paired-eye OCT images, repeated clinical measurements, and multicenter data. Eight controlled scenarios compare flawed and leakage-safe designs: seven use locked confusion matrices with auditable metrics, and one uses a reproducible repeated-study simulation. The scenarios cover global feature selection, normalization leakage, dependent records, center mixing, repeated test-set use, and estimator instability. Bias, variance, metric aggregation, uncertainty, and computational cost are also examined. A data-size matrix, a decision tree, and reporting checklists are provided. Reproducible MATLAB templates and scikit-learn counterparts are included. The results show that no validation method is universally best. The independent unit must match the intended deployment target. Every data-dependent operation must also exclude the observations used for performance estimation.
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cs.CLcs.LG Rocker D'Antonio, Thomas Benton Townsend, Dimitrios Michael Manias · Oct 1, 2026

Technical documentation preserves collaborative context, but sentence-level specificity predictors were trained on general-domain prose. This paper audits whether two such predictors—SpeciTeller and a pinned post-publication implementation of Ko et al.'s domain-adapted model—produce stable, useful signals when applied to technical corpora (GitHub, Ansible, Python docs) and used to rank LLM-generated revisions. Using a three-stage evidence structure, the authors separate score interpretation, local correspondence with humans and controlled edits, and bounded decision value for post-generation candidate selection.

Collaboration depends on shared context, and technical documentation is one way that context persists across people and AI teammates. Specificity, the amount and exactness of detail expressed in language, shapes what information documentation captures and how precisely that information is communicated. This work audits sentence-specificity scoring artifacts on technical documentation and tests whether scores applied only after generation help choose among fixed LLM-generated revisions. Across Wikipedia and three technical-documentation corpora, the fixed general-domain predictor SpeciTeller and the pinned post-publication author-repository implementation of Ko et al.'s target-adapted predictor produce different corpus orders and same-sentence rank agreement from -0.066 to 0.510. Strict filtering and token-length adjustment change these patterns without reconciling them. In the Gemma set, SpeciTeller ranking raises direction-valid selection from 71.7% to 83.3% (+11.7 points; 95% source-case bootstrap interval +1.7 to +21.7); in the GPT-OSS-120B set, SpeciTeller ranking raises direction-valid selection from 51.7% to 56.7% (+5.0 points; 95% source-case bootstrap interval -6.7 to +16.7), and every primary single-score GPT-OSS-120B interval includes zero. These findings tie score interpretation and decision value to the predictor and candidate set.
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cs.ROcs.LGcs.MA Yifan Hu, Luhang Hong, Mingkang Long et al. · Oct 1, 2026

Coordinated multi-humanoid loco-manipulation is notoriously difficult because it couples high-dimensional whole-body control with decentralized decision making and scalability. MASkillBlender addresses this by learning a shared decentralized high-level multi-agent RL policy that blends frozen, pre-trained single-humanoid primitive skills, eliminating the need for task-specific motion references or painstaking per-task reward engineering. The authors further introduce a permutation-based data augmentation strategy and prove, under a homogeneous Markov game formulation, that it preserves the policy-gradient direction. Simulated experiments across cooperative manipulation and locomotion tasks suggest broad versatility across robot embodiments and simulators, though the work stops short of real-world validation and is limited to small, homogeneous teams.

Coordinated multi-humanoid loco-manipulation is promising yet challenging due to high-dimensional whole-body control, decentralized decision making, and scalability. While recent reinforcement learning methods have improved single-humanoid whole-body control, extending them to the multi-humanoid setting remains nontrivial and often requires substantial reward engineering or task-specific design. We propose MASkillBlender, a general multi-agent reinforcement learning framework to achieve decentralized multi-humanoid whole-body coordination. By learning a shared decentralized high-level policy over reusable pre-trained single-humanoid skills, MASkillBlender enables coordinated behaviors using only task-level rewards, without requiring task-specific motion references. To improve learning efficiency, we further introduce a permutation-based data augmentation strategy for homogeneous multi-humanoid systems, and theoretically show that the permuted samples preserve the policy-gradient direction of the original samples under the homogeneous Markov game formulation. We evaluate MASkillBlender on multiple multi-humanoid coordination tasks across two humanoid embodiments. Simulation results demonstrate that the proposed framework consistently achieves strong task performance and enables coordinated behaviors across different tasks and humanoid embodiments.
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cs.LG Jimin Seo, Gyubok Lee, Yeonsik Jo et al. · Oct 1, 2026

Training hybrid Transformer-SSM models requires expensive per-scale learning rate (LR) tuning. This paper empirically shows that "naïve" Maximal Update Parameterization (μP) — as originally prescribed for pure Transformers, with no SSM-specific modifications — combined with AdamW achieves near-zero LR transfer gap across hybrid architectures from width 256 to 2048 (8×) and depth 4 to 32 (8×), up to billion parameters and on a production Nemotron-H model. The authors propose a two-condition decomposition (global update-to-weight invariance from μP, local per-component balance from AdamW's g/√v normalization) to explain why coordinate checks fail while transfer still succeeds.

We study learning rate (LR) scaling for hybrid architectures combining Transformer and State-Space Model (SSM) blocks, a class adopted by several recent production language models. In particular, we focus on the gap between the theoretical scaling rules derived for SSMs under zero-order-hold (ZOH) discretization at infinite width with growing state size, and the field-standard practical implementations using simplified-ZOH Mamba at fixed state size. Surprisingly, in this practical regime hybrid architectures achieve a near-zero LR transfer gap across widths 256-2048 and depths 4-32 up to billion-parameter scale using only the original $\mu$P prescription, even though SSM operations fall outside its Tensor Programs representability conditions and every parameterization we test fails the standard coordinate-check diagnostic of $\mu$P correctness. We attribute this to a two-condition decomposition of LR transfer in hybrid architectures: a global update-to-weight invariance, enforced by $\mu$P's initialization and LR scaling; and a local per-component balance, provided by AdamW's per-parameter normalization. Our observations show that the optimal LR is invariant to width up to 8$\times$, that this width invariance holds across depth, sequence length, batch size, and Transformer-to-SSM ratio, and that it transfers to Nemotron-H, a production hybrid outside our custom architecture set. We hope these findings fill the gap between theoretical scaling rules and practical hybrid implementations, and stimulate further research toward bridging it.
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cs.LG Seongcheol Jeong, Masahiro Suzuki, Yutaka Matsuo · Oct 1, 2026

Model merging for LLMs typically requires expensive benchmark evaluations to tune combination coefficients. This paper proposes SLIM, which treats coefficient selection as a classical mixture experiment on the simplex. It builds a quadratic surrogate of aggregate performance using only $T(T+1)/2$ evaluations—individual experts and equal-weight pairs—then optimizes the surrogate without further measurements. The core finding is that this minimal structured design predicts unseen mixtures accurately and yields competitive merges at a fraction of the cost of evolutionary or surrogate baselines, though restricting coefficients to the simplex may limit absolute performance.

Optimizing merging coefficients for large language models can require many costly benchmark evaluations. We propose \textbf{Simplex-Lattice Interpolation Merging (SLIM)}, which constructs a quadratic surrogate of aggregate performance on the coefficient simplex using a classical mixture design. Evaluations of individual experts and equal-weight pairs determine the surrogate with the minimum number of measurements needed to identify a general quadratic on this domain. SLIM then optimizes the surrogate without further target-metric evaluations. Experiments on two model architectures demonstrate accurate prediction of unseen multi-expert mixtures and competitive merge performance under limited evaluation budgets. Matched-budget comparisons show that structured evaluation points improve prediction fidelity over random designs, including those using regularized fitting.
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cs.LGcs.AImath.ST Yunrui Guan, Krishnakumar Balasubramanian, Shiva Prasad Kasiviswanathan · Oct 1, 2026

Counterfactual generation aims to sample the distribution of outcomes that would occur if a treatment were applied to an entire population, but observational data suffer from selection bias because treated individuals differ systematically from the target population. This paper develops a flow-matching method that learns to transport observed outcomes to counterfactual targets using a learned source-target coupling, a doubly robust training objective, and a score-corrected stochastic sampler with Gaussian smoothing. The core theoretical result is a finite-step KL bound governed by the coupling displacement moment $D_5$ rather than worst-case regularity, yielding near-linear dimension scaling and an end-to-end nonparametric sample-complexity guarantee; experiments on synthetic and semi-synthetic image data support the predicted coupling dependence and show that stochastic sampling can outperform deterministic counterparts at limited discretization budgets.

Counterfactual generation seeks to sample outcomes under a hypothetical intervention or decision using observational data collected under the factual assignment mechanism. We develop a flow-matching approach that combines a sample-split, doubly robust training objective with a learned coupling between observed source outcomes and target outcomes drawn from a fitted conditional outcome model. To enable finite-step generation, we leverage a score-corrected stochastic sampler based on a Gaussian-smoothed interpolation. Our main theoretical contribution is a coupling-sensitive KL bound for constant-step Euler discretization: the error is controlled by moments of the source--target displacement under the chosen coupling, rather than by global uniform regularity of the velocity field, and has near-linear dependence on the ambient dimension. We also establish finite-sample non-parametric guarantees for the learned velocity and score fields when both the conditional outcome model and the source-target coupling are estimated from data. These bounds separate approximation, coupling-replacement, nuisance-estimation, generalization, and Monte Carlo errors and, combined with the sampler analysis, yield an end-to-end guarantee for counterfactual generation. Experiments on synthetic and semi-synthetic image benchmarks support the coupling-dependent theory and show that, at finite discretization budgets, the stochastic sampler can outperform the corresponding deterministic ODE sampler.
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cs.LGcs.AIcs.DB Roberto Stanzione, Jules Barbe, Magali Parrino et al. · Oct 1, 2026

Time series anomaly detection benchmarks traditionally optimize for detection accuracy while neglecting explainability and interpretability. This paper introduces SHAD, a real-world benchmark comprising 215 high-dimensional multivariate time series collected from distributed cloud storage systems, complete with per-dimension labels and rich semantic annotations. The authors evaluate 18 detection algorithms, probe spatial attribution for explainability, and test frozen LLMs for interpretability, demonstrating that accurate detection does not guarantee diagnostic utility and that zero-shot semantic interpretation remains largely unresolved.

Time Series Anomaly Detection has received increasing attention, driven by the growing availability of complex time series data. This surge has led to the development of numerous detection methods, as well as a variety of benchmarks aimed at thoroughly evaluating their performance. However, most existing detectors remain largely agnostic to domain context, overlooking explainability and interpretability. One of the main reasons for this gap is that current benchmarks primarily focus on detection accuracy, and only few of them evaluate spatial explainability. Moreover, no benchmark currently provides sufficiently rich semantic annotations to support the generation of human-understandable interpretations of anomalies. To address these limitations, we introduce SHAD (Scality High-dimensional Anomaly Detection benchmark), a fully annotated benchmark composed of 215 multivariate, high-dimensional time series collected from real-world distributed cloud storage systems operated by Scality. The proposed dataset includes rich contextual information, covering three families of anomalies with varying degrees of severity. As further contribution, we provide a foundation for future work by evaluating baseline methods for Detection, Explainability, and Interpretability, covering all stages of a TSAD pipeline. For Detection, we benchmark a wide range of existing anomaly detectors, testing their effectiveness on the proposed real-world dataset. Then, we consider explainability by evaluating whether measuring the contribution of each dimension in the generated anomaly score can provide accurate anomaly attributions. Finally, for interpretability, we investigate the effectiveness of frozen LLM baselines in localizing and interpreting anomalies.
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cs.LGcs.CL Shengye Tao, Yinzhu Cheng, Haihua Xie · Oct 1, 2026

Most interpretability studies ablate or probe a single training checkpoint, leaving it unclear whether observed depth-dependent sensitivities are stable or transient. This paper tracks whole-block identity bypass across five released pretraining trajectories and eleven model-domain combinations to ask what persists and what shifts. The core finding is that the relative depth ordering of block sensitivities remains recognizable even as the magnitudes redistribute, and that the intervention pathway itself evolves differently across models and perturbation scales. The work matters because it cautions against treating single-checkpoint ablation profiles as static descriptions of a model's internal organization.

Layer interventions are widely used to probe the internal organization of language models, yet most analyses examine a single training checkpoint even though model representations and computations evolve throughout pretraining. This leaves open which depth-dependent intervention responses reflect persistent organization and which are transient consequences of training. We study this question using single-block identity bypass on fixed teacher-forced contexts across five released trajectories and 11 model-domain combinations. We find that block-bypass responses retain recognizable depth ordering while their magnitudes redistribute: nearby checkpoints preserve stronger rank correspondence than distant ones, and large changes concentrate at positions that recur across text samples and transfer across evaluation domains. Controlled experiments further show that changes in the natural bypass effect cannot be reduced to a single downstream sensitivity: in replicated Pythia runs, local missing-update magnitude grows while the pooled matched downstream response decreases, whereas OLMo-2 7B exhibits a different balance. These matched responses also depend on perturbation strength and direction, without identifying targeted compensation. Together, our results show that longitudinal layer sensitivity is structured but not static, and that single-checkpoint intervention responses should be interpreted in the context of how the underlying perturbation pathway evolves during training.
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stat.MEcs.LGmath.ST Hansheng Jiang · Oct 1, 2026

The nonparametric maximum likelihood estimator (NPMLE) of a Gaussian mixture is a convex program over an infinite-dimensional space, yet its maximizers can be nonunique and are only known to have at most $n$ atoms. This paper shows that a vanishingly small random reweighting of the likelihood---using independent Gamma weights that concentrate around one---selects a unique maximizer with polylogarithmically many atoms in any fixed dimension $d$. The resulting estimator retains a Hellinger rate that is parametric up to logarithmic factors, solving the open problem of exact sparsity for multivariate Gaussian NPMLEs without any support penalty.

The nonparametric maximum likelihood estimator (NPMLE) of a Gaussian location mixture maximizes the likelihood over the infinite-dimensional space of mixing distributions. The maximizing mixing distribution can be nonunique, and the classical bound on its number of atoms grows linearly with the sample size $n$. We show that a vanishingly small random perturbation of the likelihood yields exact polylogarithmic sparsity. The resulting randomly reweighted NPMLE maximizes a weighted likelihood whose independent weights, taken to be Gamma in our analysis, concentrate around one as $n$ grows. With high probability, it is unique, has $O\{(\log n/\log\log n)^d+\log n\}$ atoms in dimension $d$, nearly maximizes the ordinary likelihood, and estimates the mixture density at a Hellinger rate that is parametric up to logarithmic factors. This sparsity holds for the estimator itself, not for an approximation of it, and requires no support penalty. The proof rests on an effective-dimension principle for positive kernel mixtures: low-dimensional variation of the fitted values controls the support of every extreme point of the set of maximizers. Numerical illustrations verify that the reweighted NPMLE has Hellinger risk and support size comparable to those of the ordinary NPMLE.
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cs.LGcs.AI Di He, Pengxiang Li, Da Chang et al. · Oct 1, 2026

Looped Transformers reuse shared blocks to scale depth without adding parameters, but MoE variants degrade beyond two loops. This paper diagnoses two bottlenecks—hidden-state drift and expert selection collapse—and proposes LOOM, combining residual scaling, embedding re-injection, per-loop routers, and a Looping Residual. It matters because it attempts to establish recurrent depth as a genuine, compute-efficient scaling axis for sparse LLMs.

Looped Transformers introduce recurrent depth as a new scaling axis for LLMs: by repeatedly applying shared Transformer blocks, they increase effective depth without increasing parameter count. However, the benefits of looping remain unclear for large MoE LLMs under FLOPs-matched comparisons. The main reason is that the gains from additional iterations diminish quickly and can even turn into degradation, so the extra FLOPs spent on looping yield little substantial improvement. Consequently, prior work typically settles on two loops. We identify two main obstacles to scaling looped MoE. First, looping inherits and amplifies the curse of depth: hidden-state variance grows with each iteration as residual updates accumulate, which destabilizes deep recurrence and causes representations to drift. Second, looped MoE suffers from expert selection collapse: routers repeatedly select the same experts across loops, so extra iterations add computation without adding computational diversity. Guided by this diagnosis, we propose LOOM, built on a single principle: each loop should contribute new computation while keeping the recurrent state stable. LOOM stabilizes recurrence by scaling residual updates to bound variance growth and re-injecting the input embedding at every loop, and diversifies it through per-loop routers that engage different experts and a Looping Residual that carries earlier outputs forward. Experiments across 100M-1.7B models show stable scaling to 9-12 loops. Under near-iso-FLOP, the 700M model performs best at 5 loops, reducing perplexity from 18.36 to 16.54 and improving average zero-shot accuracy from 38.84% to 39.53% over the non-looped baseline. Without FLOP matching, the 1.7B model trained on 60B tokens peaks at 9 loops, reducing perplexity from 9.62 to 7.77 and improving average zero-shot accuracy from 42.4% to 47.7%. Code is available https://github.com/hed-ucas/LOOM.