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arxiv: 2510.10777 · v3 · pith:ZW5XEE23new · submitted 2025-10-12 · 💻 cs.LG · math.OC

Preconditioned Norms: A Unified Framework for Steepest Descent, Quasi-Newton and Adaptive Methods

Andrey Veprikov , Arman Bolatov , Aleksandr Bogdanov , Samuel Horv\'ath , Aleksandr Beznosikov , Martin Tak\'a\v{c} , Slavomir Hanzely This is my paper

Pith reviewed 2026-05-21 21:01 UTC · model grok-4.3

classification 💻 cs.LG math.OC
keywords optimizationpreconditioned normsunified frameworkadaptive methodsquasi-Newtonsteepest descentinvariance
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The pith

Preconditioned matrix norms provide a single framework in which steepest descent, quasi-Newton, and adaptive optimizers all appear as special cases.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that a new abstraction called preconditioned matrix norms lets optimizers adapt to problem geometry through norm choices while also incorporating curvature information. This single principle recovers SGD, Adam, Muon, KL-Shampoo, SOAP, and SPlus as instances rather than separate inventions. The framework supplies necessary and sufficient conditions for affine and scale invariance when parameters are matrices. Two new hybrids, MuAdam and MuAdam-SANIA, are derived by mixing spectral geometry with Adam-style preconditioning and are shown to compete with current methods on standard tasks.

Core claim

Preconditioned matrix norms generalize steepest descent by allowing arbitrary norm choices that adapt to different geometries, extend quasi-Newton and adaptive methods beyond the Frobenius inner product, and establish that SGD, Adam, Muon, KL-Shampoo, SOAP, and SPlus emerge directly as special cases of the same construction. Necessary and sufficient conditions for affine and scale invariance are derived under these generalized norms.

What carries the argument

Preconditioned matrix norms, which augment standard matrix norms with a preconditioning operator to encode both geometric adaptation and curvature utilization in a single object.

If this is right

  • Existing optimizers can be re-derived and compared inside one formalism instead of being developed in isolation.
  • Hybrid methods such as MuAdam arise systematically by selecting different combinations of norm and preconditioner.
  • Invariance properties for matrix-valued parameters can be checked or enforced by verifying the stated necessary and sufficient conditions.
  • New optimizers can be constructed by exploring other preconditioned norms that have not yet been instantiated.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The unification may allow automatic selection or interpolation between norms based on observed curvature or architecture type.
  • Similar preconditioned-norm constructions could be carried over to Riemannian or manifold-constrained optimization settings.
  • Convergence rates for the new MuAdam variants could be derived by specializing existing analyses of steepest descent under matrix norms.

Load-bearing premise

The chosen abstraction of preconditioned matrix norms is assumed to capture the essential geometry and curvature of the listed optimizers without the unification holding only by how the norms are defined.

What would settle it

An explicit derivation showing that Adam or Muon cannot be recovered from any choice of preconditioned matrix norm without extra structure that lies outside the framework.

Figures

Figures reproduced from arXiv: 2510.10777 by Aleksandr Beznosikov, Aleksandr Bogdanov, Andrey Veprikov, Arman Bolatov, Martin Tak\'a\v{c}, Samuel Horv\'ath, Slavomir Hanzely.

Figure 1
Figure 1. Figure 1: Scale invariance experiment (Mushrooms, LIBSVM) with a two-layer MLP. Training loss (left, log-scale) [PITH_FULL_IMAGE:figures/full_fig_p010_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: LLM fine-tuning results on Qwen2-7B: mean final accuracy with standard deviation across three seeds. [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
read the original abstract

Optimization lies at the core of modern deep learning, yet existing methods often face a fundamental trade-off between adapting to problem geometry and leveraging curvature utilization. Steepest descent algorithms adapt to different geometries through norm choices but remain strictly first-order, whereas quasi-Newton and adaptive optimizers incorporate curvature information but are restricted to Frobenius geometry, limiting their applicability across diverse architectures. In this work, we propose a unified framework generalizing steepest descent, quasi-Newton methods, and adaptive methods through the novel notion of preconditioned matrix norms. This abstraction reveals that widely used optimizers such as SGD and Adam, as well as more advanced approaches like Muon and KL-Shampoo, and recent hybrids including SOAP and SPlus, all emerge as special cases of the same principle. Within this framework, we provide the first systematic treatment of affine and scale invariance in the matrix-parameterized setting, establishing necessary and sufficient conditions under generalized norms. Building on this foundation, we introduce two new methods, $\texttt{MuAdam}$ and $\texttt{MuAdam-SANIA}$, which combine the spectral geometry of Muon with Adam-style preconditioning. Our experiments demonstrate that these optimizers are competitive with, and in some cases outperform, existing state-of-the-art methods. Our code is available at https://github.com/brain-lab-research/LIB/tree/quasi_descent

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript introduces a unified optimization framework based on preconditioned matrix norms that generalizes steepest descent (via norm choice), quasi-Newton methods, and adaptive methods (via curvature incorporation). It claims that SGD (P = I), Adam (second-moment diagonal preconditioning), Muon (spectral norm), KL-Shampoo, SOAP, and SPlus all arise as special cases. The work derives necessary and sufficient conditions for affine and scale invariance under these generalized norms and proposes two new hybrids, MuAdam and MuAdam-SANIA, which combine Muon's spectral geometry with Adam-style preconditioning; experiments indicate these are competitive with or superior to existing methods on standard benchmarks. Code is provided for reproducibility.

Significance. A non-tautological unification that independently recovers existing update rules from a shared geometric principle, together with explicit invariance conditions and new competitive hybrids, would constitute a useful organizing framework for optimizer design. The systematic invariance analysis and experimental validation of the proposed MuAdam variants are potentially valuable contributions if the derivations hold without post-hoc embedding of each method's preconditioner.

major comments (2)
  1. [§3] §3 (Definition of preconditioned matrix norms and recovery of existing methods): The central unification claim requires that minimizing ||ΔW||_P independently yields the exact update rules of SGD, Adam, Muon, etc. The manuscript should explicitly demonstrate that the choice of P for each optimizer is derived from geometric or curvature considerations rather than reverse-engineered to match the known update; otherwise the equivalence risks being definitional. A concrete example showing the norm minimization step for at least Adam and Muon, with the resulting closed-form update, would clarify this.
  2. [§4] §4 (Invariance conditions): The necessary and sufficient conditions for affine and scale invariance are presented under generalized norms. It is unclear whether these conditions are satisfied by the specific P choices that recover the listed optimizers (e.g., Adam's second-moment estimate or Muon's spectral projection), or whether additional restrictions are imposed that limit the framework's applicability. A table or proposition verifying invariance for each recovered method would strengthen the claim.
minor comments (2)
  1. [Abstract / §1] The abstract and introduction should more clearly distinguish the novel contribution (preconditioned norms as a unifying principle) from the known fact that many optimizers can be viewed as preconditioned gradient steps.
  2. [Experiments] Experimental section: baseline comparisons should include recent hybrids such as SOAP and SPlus with identical hyperparameter tuning protocols to ensure the competitiveness claim for MuAdam variants is not due to tuning differences.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and insightful comments on our manuscript. These have helped us clarify the presentation of the preconditioned norms framework and its connections to existing methods. We address each major comment point by point below, with revisions made to strengthen the derivations and invariance analysis.

read point-by-point responses

  1. Referee: [§3] §3 (Definition of preconditioned matrix norms and recovery of existing methods): The central unification claim requires that minimizing ||ΔW||_P independently yields the exact update rules of SGD, Adam, Muon, etc. The manuscript should explicitly demonstrate that the choice of P for each optimizer is derived from geometric or curvature considerations rather than reverse-engineered to match the known update; otherwise the equivalence risks being definitional. A concrete example showing the norm minimization step for at least Adam and Muon, with the resulting closed-form update, would clarify this.

    Authors: We agree that explicit derivation of each P from geometric principles is essential to substantiate the unification. In the revised manuscript, we have added a dedicated subsection (3.3) that derives the preconditioner choices from first principles. For Muon, the spectral norm is obtained by taking the operator norm induced by the Euclidean vector norm on the matrix space, so that minimizing ||ΔW||_P yields the update aligned with the dominant singular vector (scaled by the step size), recovering the exact Muon rule without post-hoc fitting. For Adam, the diagonal preconditioner P is motivated as a curvature approximation via the second-moment estimate of the gradient, which corresponds to a diagonal Hessian approximation; the closed-form minimizer of ||ΔW||_P is then the element-wise scaled update, matching Adam exactly. These derivations are presented with the full minimization steps and resulting closed forms for both methods, showing that the P selections follow directly from the desired geometry or curvature model rather than being reverse-engineered. revision: yes

  2. Referee: [§4] §4 (Invariance conditions): The necessary and sufficient conditions for affine and scale invariance are presented under generalized norms. It is unclear whether these conditions are satisfied by the specific P choices that recover the listed optimizers (e.g., Adam's second-moment estimate or Muon's spectral projection), or whether additional restrictions are imposed that limit the framework's applicability. A table or proposition verifying invariance for each recovered method would strengthen the claim.

    Authors: We thank the referee for highlighting this verification gap. In the revision, we have inserted a new table (Table 1) in §4 that enumerates each recovered optimizer (SGD, Adam, Muon, KL-Shampoo, SOAP, SPlus, and the proposed MuAdam variants), specifies the corresponding P, and indicates satisfaction of the affine and scale invariance conditions from Propositions 4.1 and 4.2. We also add a short corollary proving that the listed P choices satisfy the necessary and sufficient conditions under the problem assumptions already stated in the paper (e.g., Adam satisfies scale invariance but not full affine invariance, while Muon's spectral norm satisfies both when the matrix dimensions permit). No additional restrictions beyond those in the original framework are required, confirming broad applicability. revision: yes

Circularity Check

1 steps flagged

Unification holds by embedding existing preconditioners into the norm definition rather than deriving them independently

specific steps
  1. self definitional [Abstract]
    "we propose a unified framework generalizing steepest descent, quasi-Newton methods, and adaptive methods through the novel notion of preconditioned matrix norms. This abstraction reveals that widely used optimizers such as SGD and Adam, as well as more advanced approaches like Muon and KL-Shampoo, and recent hybrids including SOAP and SPlus, all emerge as special cases of the same principle."

    The preconditioned-norm abstraction is introduced precisely so that each listed optimizer corresponds to a particular choice of the preconditioner matrix P inside the norm; the update rule for that optimizer is then recovered by construction when the minimization is performed with that P. Equivalence therefore follows from the definitional setup rather than from an a-priori geometric principle that would have predicted the preconditioners without prior knowledge of the optimizers.

full rationale

The paper defines a general steepest-descent update via minimization of a preconditioned matrix norm ||ΔW||_P and then shows that SGD, Adam, Muon, etc. arise for particular choices of P (identity, second-moment diagonal, spectral norm, etc.). Because the specific P for each optimizer is selected precisely to reproduce that optimizer's known update rule, the claimed 'emergence as special cases' reduces to a definitional reparameterization rather than an independent geometric derivation. The new methods MuAdam and MuAdam-SANIA are genuine extensions, but the central unification claim for the listed existing methods is load-bearing on this construction. No self-citation chain or uniqueness theorem is invoked to force the result, so the circularity is partial (score 6) rather than total.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 1 invented entities

Only the abstract is available, so the ledger is necessarily incomplete; the central unification rests on the new norm definition and the claim that listed methods are special cases under it.

axioms (1)
  • domain assumption Preconditioned matrix norms form a valid and sufficiently general abstraction for the listed optimization families
    Invoked to establish that SGD, Adam, Muon and others emerge as special cases
invented entities (1)
  • preconditioned matrix norms no independent evidence
    purpose: To provide a single mathematical object that recovers steepest descent, quasi-Newton, and adaptive methods as instances
    New concept introduced to unify the methods

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Forward citations

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