Universal and Parameter-free Gradient Sliding for Composite Optimization
Pith reviewed 2026-05-21 10:21 UTC · model grok-4.3
The pith
PFUGS solves convex composite optimization to ε-accuracy using O((M_ν/ε)^{2/(1+3ν)}) subgradient calls for f and O((L/ε)^{1/2}) gradient calls for g, with no knowledge of the constants M_ν, ν or L.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The PFUGS algorithm computes an ε-approximate solution to the convex composite optimization problem min_{x in X} {f(x) + g(x)} with O((M_ν/ε)^{2/(1+3ν)}) evaluations of (sub)gradients of f and O((L/ε)^{1/2}) evaluations of gradients of g, without prior knowledge of the problem constants M_ν, ν, and L.
What carries the argument
The Parameter-Free Universal Gradient Sliding (PFUGS) algorithm, which combines a universal gradient step for the Hölder part f with a sliding inner loop for the smooth part g and uses observed gradient norms to adapt step sizes on the fly.
If this is right
- The algorithm attains the optimal complexity known for the Hölder-smooth term f while treating its parameters as unknown.
- It simultaneously attains the optimal complexity known for the smooth term g while treating its Lipschitz constant as unknown.
- No separate tuning or restarting phase is required to achieve both rates at once.
- The method extends gradient sliding to the setting in which the two summands have genuinely different and a priori unknown smoothness classes.
Where Pith is reading between the lines
- The same adaptive sliding structure could be tested on problems with three or more summands by cycling through pairwise slides.
- Because the method never needs the constants, it may serve as a drop-in solver for black-box composite problems arising in machine learning where smoothness parameters change with data.
- A natural next measurement would be the practical wall-clock time on large-scale instances compared with restarted or tuned baselines.
Load-bearing premise
The functions must obey the given Hölder subgradient condition on f and Lipschitz gradient condition on g, and the adaptive rule inside PFUGS must recover the claimed complexity bounds even though it never receives the numerical values of M_ν, ν, or L.
What would settle it
Implement PFUGS on a simple quadratic or Hölder example where the exact constants M_ν, ν, and L are known in closed form, run it with only gradient oracles and no constant inputs, and verify whether the observed number of calls stays within the stated big-O bounds for a sequence of decreasing ε.
read the original abstract
We propose a Parameter-Free Universal Gradient Sliding (PFUGS) algorithm for computing an approximate solution to the convex composite optimization $\min_{x\in X} \{f(x) + g(x)\}$, where $f$ has $(M_\nu,\nu)$-H\"older continuous subgradient and $g$ has $L$-Lipschitz continuous gradient. PFUGS computes an $\varepsilon$-approximate solution with $\mathcal{O}((M_\nu/\varepsilon)^{{2}/{(1+3\nu)}})$ evaluations of (sub)gradients of $f$ and $\mathcal{O}((L/\varepsilon)^{1/2})$ evaluations of gradients of $g$, without prior knowledge of problem constants. To the best of our knowledge, PFUGS is the first gradient sliding algorithm for problems involving two functions whose distinct problem constants are both unknown a priori.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes the Parameter-Free Universal Gradient Sliding (PFUGS) algorithm for the convex composite problem min_{x in X} {f(x) + g(x)}, where f satisfies the (M_ν, ν)-Hölder continuous subgradient condition and g has L-Lipschitz continuous gradients. PFUGS is claimed to return an ε-approximate solution using O((M_ν/ε)^{2/(1+3ν)}) (sub)gradient evaluations of f and O((L/ε)^{1/2}) gradient evaluations of g, without any prior knowledge of M_ν or L. The authors state that this is the first gradient-sliding method in which both distinct problem constants are unknown a priori.
Significance. If the stated complexity bounds hold, the result would be a useful practical advance: it removes the need to estimate or tune two separate constants that are often difficult to obtain in applications. The work extends existing gradient-sliding frameworks to a fully parameter-free regime while preserving the optimal exponents for the Hölder and smooth components, which could serve as a template for other composite or multi-function settings.
minor comments (4)
- §2.1: the precise statement of the (M_ν, ν)-Hölder condition on the subgradient of f should include the domain restriction and the constant M_ν explicitly, to avoid ambiguity when the algorithm later estimates this quantity.
- Algorithm 1 (PFUGS pseudocode): the inner-loop termination criterion and the doubling-search rule for estimating M_ν are presented without an accompanying line-by-line complexity accounting; a short table or remark summarizing the per-phase cost would improve readability.
- Theorem 3.1: the proof sketch invokes a standard potential-function argument, but the transition from the estimated constants to the final bound is only outlined; adding one or two intermediate lemmas that bound the number of failed doubling phases would make the argument self-contained.
- §4 (numerical experiments): the test problems use synthetic data with known constants; a brief discussion of how the method behaves when the true M_ν and L are replaced by crude upper bounds would strengthen the practical claim.
Simulated Author's Rebuttal
We thank the referee for the positive assessment of our work and the recommendation for minor revision. The report correctly summarizes the contributions of PFUGS as the first parameter-free gradient sliding method for composite convex optimization with unknown Hölder and Lipschitz constants. We address the points raised below.
Circularity Check
No significant circularity
full rationale
The paper proposes PFUGS as a parameter-free extension of gradient sliding methods for composite convex optimization under Hölder and Lipschitz assumptions. The claimed complexity bounds are derived from standard adaptive techniques (such as doubling searches or restarts) applied to the distinct constants of f and g, without any reduction of the target rates to fitted parameters, self-definitions, or load-bearing self-citations. The derivation remains self-contained against external benchmarks for gradient sliding and parameter-free adaptation, with no steps that equate outputs to inputs by construction.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption f has (M_ν, ν)-Hölder continuous subgradient and g has L-Lipschitz continuous gradient.
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquation.leanwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
PFUGS computes an ε-approximate solution with O((M_ν/ε)^{2/(1+3ν)}) evaluations of (sub)gradients of f and O((L/ε)^{1/2}) evaluations of gradients of g, without prior knowledge of problem constants
-
IndisputableMonolith/Foundation/BranchSelection.leanbranch_selection unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the modified subroutine ... updates the total number of iterations on the fly ... η_s^k ∑ 1/p_t,s^k stays invariant
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
Ekaterina Borodich and Dmitry Kovalev. Nesterov finds graal: Optimal and adap- tive gradient method for convex optimization.arXiv preprint arXiv:2507.09823, 2025
-
[2]
Y. Chen, G. Lan, Y. Ouyang, and W. Zhang. Fast bundle-level methods for un- constrained and ball-constrained convex optimization.Computational Optimization and Applications, 73(1):159–199, 2019
work page 2019
-
[3]
Yunmei Chen, Xiaojing Ye, and Wei Zhang. Acceleration techniques for level bun- dle methods in weakly smooth convex constrained optimization.Computational Optimization and Applications, 77(2):411–432, 2020
work page 2020
-
[4]
Qi Deng, Guanghui Lan, and Zhenwei Lin. Uniformly optimal and parameter- free first-order methods for convex and function-constrained optimization.arXiv preprint arXiv:2412.06319, 2024
work page internal anchor Pith review Pith/arXiv arXiv 2024
-
[5]
Vincent Guigues, Jiaming Liang, and Renato D. C. Monteiro. Universal subgradient and proximal bundle methods for convex and strongly convex hybrid composite optimization.Journal of Optimization Theory and Applications, 208:112, 2026. Universal and Parameter-free Gradient Sliding
work page 2026
-
[6]
Vincent Guigues, Renato D. C. Monteiro, and Benoit Tran. Complexity and numer- ical experiments of a new adaptive generic proximal bundle method.arXiv preprint arXiv:2410.11066, 2024
work page internal anchor Pith review Pith/arXiv arXiv 2024
-
[7]
Masaru Ito, Zhaosong Lu, and Chuan He. A parameter-free conditional gradient method for composite minimization under Hölder condition.Journal of Machine Learning Research, 24(166):1–34, 2023
work page 2023
-
[8]
G. Lan. Bundle-level type methods uniformly optimal for smooth and nonsmooth convex optimization.Mathematical Programming, 149(1):1–45, 2015
work page 2015
-
[9]
Gradient sliding for composite optimization.Mathematical Pro- gramming, 159(1):201–235, 2016
Guanghui Lan. Gradient sliding for composite optimization.Mathematical Pro- gramming, 159(1):201–235, 2016
work page 2016
-
[10]
Springer, Cham, Switzerland, 2020
Guanghui Lan.First-order and stochastic optimization methods for machine learn- ing. Springer, Cham, Switzerland, 2020
work page 2020
- [11]
-
[12]
Guanghui Lan, Tianjiao Li, and Yangyang Xu. Projected gradient methods for non- convex and stochastic optimization: new complexities and auto-conditioned step- sizes.arXiv preprint arXiv:2412.14291, 2024
work page internal anchor Pith review Pith/arXiv arXiv 2024
-
[13]
Guanghui Lan and Yuyuan Ouyang. Accelerated gradient sliding for structured convex optimization.Computational Optimization and Applications, 82(2):361–394, 2022
work page 2022
-
[14]
Guanghui Lan, Yuyuan Ouyang, and Zhe Zhang. Optimal and parameter-free gra- dient minimization methods for convex and nonconvex optimization.arXiv preprint arXiv:2310.12139, 2023
-
[15]
Tianjiao Li and Guanghui Lan. A simple uniformly optimal method without line search for convex optimization.Mathematical Programming, pages 1–38, 2025
work page 2025
-
[16]
Zhaosong Lu and Sanyou Mei. Accelerated first-order methods for convex opti- mization with locally lipschitz continuous gradient.SIAM Journal on Optimization, 33(3):2275–2310, 2023
work page 2023
-
[17]
Zhaosong Lu and Sanyou Mei. Primal-dual extrapolation methods for monotone inclusions under local lipschitz continuity.Mathematics of Operations Research, 50(4):2577–2599, 2025
work page 2025
-
[18]
Adaptive gradient descent without descent
Yura Malitsky and Konstantin Mishchenko. Adaptive gradient descent without descent. InProceedings of the 37th International Conference on Machine Learning, volume 119 ofProceedings of Machine Learning Research, pages 6702–6712. PMLR, 2020. Universal and Parameter-free Gradient Sliding
work page 2020
-
[19]
Adaptive proximal gradient method for convex optimization
Yura Malitsky and Konstantin Mishchenko. Adaptive proximal gradient method for convex optimization. InAdvances in Neural Information Processing Systems, volume 37, 2024
work page 2024
-
[20]
Renato D. C. Monteiro, Camilo Ortiz, and Benar F. Svaiter. An adaptive acceler- ated first-order method for convex optimization.Computational Optimization and Applications, 64(1):31–73, 2016
work page 2016
- [21]
-
[22]
Y. E. Nesterov. A method for unconstrained convex minimization problem with the rate of convergenceO(1/k2).Doklady AN SSSR, 269:543–547, 1983. translated as Soviet Math. Docl
work page 1983
-
[23]
Y. E. Nesterov. Universal gradient methods for convex optimization problems. Mathematical Programming, 152(1-2):381–404, 2015
work page 2015
-
[24]
Gradient methods for minimizing composite functions.Mathematical Programming, pages 1–37, 2012
Yu Nesterov. Gradient methods for minimizing composite functions.Mathematical Programming, pages 1–37, 2012
work page 2012
-
[25]
Yuyuan Ouyang and Trevor Squires. Universal conditional gradient sliding for convex optimization.SIAM Journal on Optimization, 33(4):2962–2987, 2023
work page 2023
-
[26]
Proximal algorithms.Foundations and Trends® in Optimization, 1(3):127–239, 2014
Neal Parikh, Stephen Boyd, et al. Proximal algorithms.Foundations and Trends® in Optimization, 1(3):127–239, 2014
work page 2014
-
[27]
Jaewook J. Suh and Shiqian Ma. An adaptive and parameter-free nesterov’s accel- erated gradient method for convex optimization.arXiv preprint arXiv:2505.11670, 2025
-
[28]
Arnesh Sujanani and Renato D. C. Monteiro. Efficient parameter-free restarted accelerated gradient methods for convex and strongly convex optimization.Journal of Optimization Theory and Applications, 206:52, 2025. Universal and Parameter-free Gradient Sliding A Omitted proofs In this appendix, we present several proofs that were omitted from the main text...
work page 2025
discussion (0)
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