Daily research notes18 min read

Last iterates and ambiguous extrapolation

Finite-step Muon · Rashomon fits · IV prediction · Lottery Ticket

Two main readings and nine briefs, including one version watch: update geometry near zero and divergent extrapolations with nearly equal fitting loss. The classic separates sparse structure, initialization, and discovery cost.

MuonScaling lawsWharton facultyDeep learning theory
Daily classic · 2019Lottery Ticket Hypothesis
Main readingRead Sections 2–4, Theorem 3.2 and its proof outline; appendix not audited line by line

How does stabilization change the update near zero?

Last-Iterate Stationarity of Muon with Finitely Many Newton-Schulz Iterations
Ping Li · Vincent Y. F. Tan
First posted 2026-10-25 · v1

Let F be lower bounded with globally L-Lipschitz gradient in Frobenius norm. The paper studies finite-step NS in exact arithmetic, without weight decay, rather than replacing it by polar.[1]

Deterministic input; fixed beta in [0,1) and theta in [0,1] [1]
Mt=βMt−1+(1−β)gt,Nt=θMt+(1−θ)gt,gt=∇F(Wt)M_t=\beta M_{t-1}+(1-\beta)g_t,\quad N_t=\theta M_t+(1-\theta)g_t,\quad g_t=\nabla F(W_t)
Fixed J at least one; (a,b,c)=(3.4445,-4.7750,2.0315) [1]
Z0=Nt∥Nt∥F+ε,Zj+1=aZj+bZjZj⊤Zj+c(ZjZj⊤)2Zj,Wt+1=Wt−ηZJZ_0={N_t\over\|N_t\|_F+\varepsilon},\quad Z_{j+1}=aZ_j+bZ_jZ_j^\top Z_j+c(Z_jZ_j^\top)^2Z_j,\quad W_{t+1}=W_t-\eta Z_J

At epsilon=0, scalar normalization removes nonzero input magnitude; the paper constructs a two-cycle on a convex quadratic. Positive epsilon shrinks small-input updates and provides the sector inequality for descent–momentum tracking.[1]

Theorem 3.2; u_J is the global output-norm bound for the finite NS map in Lemma 2.2 [1]
0<η≤ε(1−β)4LuJ⟹∑t=1∞∥gt∥F2<∞,∥gt∥F→00<\eta\le {\varepsilon(1-\beta)\over4Lu_J}\quad\Longrightarrow\quad\sum_{t=1}^\infty\|g_t\|_F^2<\infty,\qquad \|g_t\|_F\to0
Main readingRead Sections 2–4, Algorithm 1 and limitations; code not run

Equal fit quality need not mean equal forecasts

Ambiguous Fits: The Rashomon Effect and Challenges in Scaling Law Estimation
Bruno Mlodozeniec · Spencer Frei
First posted 2026-10-25 · v1

Chinchilla (2022) fitting commonly uses multi-start local optimization. This paper separates global optimization accuracy from agreement among nearly optimal extrapolations.[2]

x denotes resource axes, y observed loss; h_delta is Huber loss with threshold delta [2]
L(x;ϑ)=E+∑i=1kAixi−αi,R(ϑ)=∑nhδ ⁣(log⁡L(xn;ϑ)−log⁡yn)L(x;\vartheta)=E+\sum_{i=1}^k A_ix_i^{-\alpha_i},\qquad R(\vartheta)=\sum_n h_\delta\!\left(\log L(x_n;\vartheta)-\log y_n\right)
Notation for explanation: Theta is a declared compact domain; the envelope covers predictions of near-optimal fits [2]
Sϵ={ϑ∈Θ:R(ϑ)≤inf⁡ΘR+ϵ},[L−(x∗),L+(x∗)]=[inf⁡SϵL(x∗;ϑ),sup⁡SϵL(x∗;ϑ)]\mathcal S_\epsilon=\{\vartheta\in\Theta:R(\vartheta)\le\inf_{\Theta}R+\epsilon\},\qquad [L_-(x_*),L_+(x_*)]=\left[\inf_{\mathcal S_\epsilon}L(x_*;\vartheta),\sup_{\mathcal S_\epsilon}L(x_*;\vartheta)\right]

A monotone reparameterization bounds residuals over parameter boxes. Branch-and-bound splits promising boxes and discards those whose lower bounds cannot beat the incumbent. Stopping certifies its gap to a global lower bound. Four real scaling ladders demonstrate divergent extrapolation with nearly equal fit error.[2]

BriefBased on abstract and version history; not reproduced

Mix layers, then polarize slices

A unitary transform mixes layers before slice-wise polarization and inverse transformation. Authors characterize steepest descent in a transformed tensor spectral norm. Theorems and matched budgets were not checked; no speedup magnitude is reported here.[3]

BriefBased on abstract and version history; not reproduced

Predictability also depends on the RL metric

An Empirical Study of Reinforcement Learning Scaling Laws
Zeyu Zheng · Clare Lyle · Khimya Khetarpal · Will Dabney
First posted 2026-10-23 23:29 New York time · v1; delayed-index catch-up

In Starpilot and Craftax actor–critic experiments, authors find a single-agent Elo variant more predictable than mean return and report extrapolation across two orders of magnitude in compute. Craftax compute-optimal model size can be non-monotone. Fit/extrapolation splits were not checked.[4]

BriefBased on abstract and version history; not reproduced

An information scale for memorization and sample quality

Information-Theoretic Scaling Laws for Generative Diffusion Training
Druv Pai · Dejan Stancevic · Yi Ma · Luca Ambrogioni
First posted 2026-10-23 18:21 New York time · v1; delayed-index catch-up

Model information measures sample dependence on the particular training dataset. Authors posit two scaling regimes and derive induced laws for memorization and quality. This is a proposed, empirically fitted law; the abstract does not establish universality.[5]

BriefBased on abstract and version history; not reproduced

Depth benefits depend on the task spectrum

Depth Improves Training-Time Scaling for Difficult Tasks in Deep Linear Networks
Taishi Watanabe · Ryo Karakida · Jun-nosuke Teramae
2026-10-26 · v1

In deep linear networks, depth improves the training-time exponent for difficult tasks but not easy ones; predictor-norm time reparameterization yields a common law. Abstract only: initialization, spectral conditions and nonlinear numerical evidence were not checked in detail.[6]

BriefBased on abstract and version history; not reproduced

When is MNAR prediction informative?

Distribution-free predictive inference with instrumental variables
Yonghoon Lee · Edgar Dobriban · Eric Tchetgen Tchetgen
2026-10-26 · v1

Wharton author subscription: an identification index separates impossibility from informative prediction with MNAR outcomes and instrumental variables. Efficient influence functions support doubly robust coverage. Abstract only; this does not remove the need for identifying assumptions.[7]

BriefBased on abstract and version history; not reproduced

Model survival probability ratios directly

Towards the Revival of Survival Ratio
Ruixuan Zhao · Jingxin Yan · Xiaochuan Shi · Torben Martinussen · Eric Tchetgen Tchetgen · Linbo Wang
2026-10-25 New York time · v1

Wharton author subscription: survival and cumulative-incidence ratios are targeted with variation-independent nuisance parameters and valid monotone curves, supporting likelihood and doubly robust estimation. Abstract only; descriptive selected-cohort results are not causal effects.[8]

BriefBased on abstract and version history; not reproduced

Version watch: width, connectivity and unit complexity

Scaling Laws and Tradeoffs in Recurrent Networks of Expressive Neurons
Aaron Spieler · Georg Martius · Anna Levina
First posted 2026-05-12; v2 dated 2026-10-26; substantive version differences not verified

The current abstract studies allocation among unit count, effective per-unit complexity and connectivity at fixed parameter budget, observing an interior tradeoff on SHD-Adding and Enwik8. Version watch only: changes from v1 were not established, so these are not presented as new results.[9]

BriefBased on abstract and version history; not reproduced

Best-of-N scaling depends on reward tails

Whether or Where? Tail Calibration Signals Finite-Budget Reward Hacking in Best-of-N Selection
Cheng Gui · Yihua Shao · Lei Li · Jingcai Guo · Maolin Wang
2026-10-25 · v1

Included under inference scaling: maximum proxy-reward selection increasingly probes score tails. Authors express BoN through a Beta-weighted integral of quantile-conditional true reward and propose tail calibration audits, explicitly complementing ranking accuracy. Continuity/tie assumptions were not checked.[10]

BriefBased on abstract and version history; not reproduced

Catch-up: fixed exposure, different learning weights

Beyond Data Schedule: Fast LLM Pretraining on Data Mixtures by Loss-Reweighting
Jiazheng Li · Huaqing Zhang · Jing Xu · Tianle Cai · Jingzhao Zhang
First posted 2026-10-23 00:09 New York time · v1; delayed catch-up outside the main window

Data-mixture catch-up: LARE preserves sampling exposure while adapting domain weights from running loss statistics. The abstract reports gains over a matched direct mixture at 1.5B/240B tokens. Full text not read; reweighting is distinct from changing exposure, and numerical gains are not repeated here.[11]

Daily classic · historical workRead Sections 1–4, experimental setup and reinitialization controls; an empirical hypothesis, not a general existence theorem

Sparse structure is not enough: which initialization survives?

The Lottery Ticket Hypothesis: Finding Sparse, Trainable Neural Networks
Jonathan Frankle · Michael Carbin
First posted 2018-03-09; read v5 (2019-03-04), ICLR 2019
ICLR 2019 Best Paper Award ↗

Pruning (LeCun et al., 1990; Han et al., 2015) showed that trained networks can be compressed. The lottery hypothesis asks whether the subnetwork trains independently from its original initialization. Let d count parameters and m be a fixed binary mask.[12][13]

Weights outside the mask remain zero [12]
θ0∼D,m∈{0,1}d,fm(x;θ)=f(x;m⊙θ)\theta_0\sim\mathcal D,\quad m\in\{0,1\}^d,\qquad f_m(x;\theta)=f(x;m\odot\theta)
Original hypothesis: j is the minimum-validation-loss iteration and a its test accuracy [12]
∃m:∥m∥0≪d,jm≤jdense,am≥adense\exists m:\quad \|m\|_0\ll d,\qquad j_m\le j_{\rm dense},\qquad a_m\ge a_{\rm dense}
Algorithm restatement: train, magnitude-prune, reset each round; trained values are not retained [12]
θ^(r)=Train⁡(mr⊙θ0),mr+1=mr⊙KeepLarge⁡(θ^(r)),θstart(r+1)=mr+1⊙θ0\hat\theta^{(r)}=\operatorname{Train}(m_r\odot\theta_0),\qquad m_{r+1}=m_r\odot\operatorname{KeepLarge}(\hat\theta^{(r)}),\qquad \theta_{\rm start}^{(r+1)}=m_{r+1}\odot\theta_0
Key control fixes the mask and resamples initialization, separating structure from initialization [12]
f(x;m⊙θ0)vs.f(x;m⊙θ0′),θ0′∼Df(x;m\odot\theta_0)\quad\text{vs.}\quad f(x;m\odot\theta'_0),\qquad \theta'_0\sim\mathcal D

MNIST fully connected and CIFAR10 convolutional experiments support the hypothesis. Original initialization generally beats reinitializing the same mask. Deep networks are learning-rate sensitive: VGG-19 at 0.1 did not yield winning tickets without warmup, but did with it. Iteration savings exclude repeated mask discovery.[12]

READ THE ORIGINALS

Original sources

  1. Finite NS: original algorithm and theorems
  2. Ambiguous fits: methods and limitations
  3. TUON: A Tensor-Aware Optimizer Utilizing Tensor-SVD and Polarization for Large Language Model Pretraining: abstract and versions
  4. An Empirical Study of Reinforcement Learning Scaling Laws: abstract and versions
  5. Information-Theoretic Scaling Laws for Generative Diffusion Training: abstract and versions
  6. Depth Improves Training-Time Scaling for Difficult Tasks in Deep Linear Networks: abstract and versions
  7. Distribution-free predictive inference with instrumental variables: abstract and versions
  8. Towards the Revival of Survival Ratio: abstract and versions
  9. Scaling Laws and Tradeoffs in Recurrent Networks of Expressive Neurons: abstract and versions
  10. Whether or Where? Tail Calibration Signals Finite-Budget Reward Hacking in Best-of-N Selection: abstract and versions
  11. Beyond Data Schedule: Fast LLM Pretraining on Data Mixtures by Loss-Reweighting: abstract and versions
  12. Lottery Ticket: full paper and experiments
  13. Official ICLR award record
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2026-10-24 08:15 — 2026-10-27 08:15 · America/New_York

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