arXiv Machine Learning

DP-Muon: Differentially Private Optimization via Matrix-Orthogonalized Momentum

The paper introduces DP-Muon, a differentially private optimization method that incorporates matrix‑orthogonalized momentum. It employs standard global per‑example clipping and releases a single Gaussian‑noised gradient per step, with matrix and auxiliary updates treated as post‑processing. The authors analyze the mean distortion introduced when fresh Gaussian noise passes through a nonlinear matrix map, deriving exact Gaussian heat identities and showing that for a smooth Newton‑Schulz map, the conditional output bias is reduced from second to fourth order in the noise scale. They also establish matrix‑block stationarity bounds, quantify orthogonalization error, and provide criteria for improving the upper bound, while a separate inequality captures the impact of auxiliary Adam updates. Experiments on GPT‑2 at various privacy targets demonstrate that DP‑Muon configurations outperform Adam baselines in test negative log‑likelihood.

arXiv Machine Learning
Aug 28

Muon with Finite Newton-Schulz: The Smoothing Benefit in Nonsmooth Nonconvex Optimization

The paper introduces Muon, an optimizer that uses a finite number of Newton‑Schulz iterations to approximate the polar factor for matrix‑valued parameters in large language model pretraining. It demonstrates that this finite iteration smooths the discontinuous polar map into a Lipschitz function of singular values, enabling a conversion from online learning regret to a stationarity guarantee in nonsmooth nonconvex optimization. The authors prove that a logarithmic depth in Newton‑Schulz suffices for convergence to stationary points, matching best‑known sample complexity bounds and extending the result to other spectral maps with similar smoothing properties.

By Mingyi Li, Taira Tsuchiya
arXiv Machine Learning
Sep 17

Derivative-Free Structured Updates for Muon

The paper introduces a derivative‑free framework for Muon‑style updates, replacing gradient‑based momentum with structured finite differences. Four variants—full entrywise recovery, random low‑rank surrogates, basis‑aligned rank‑one probing, and direct structured search—are explored, with basis‑aligned probing shown to be equivalent to coordinate finite differences up to scaling. Experiments on matrix regression, noisy‑gradient regression, a neural network, and a CartPole task demonstrate that random rank‑one probing can significantly reduce function evaluations, though at the expense of update accuracy, and that accurate function values can sometimes offset unreliable gradient oracles.

By Pengcheng Xie