REVIEW 3 major objections 6 minor 41 references
The paper proves that the adaptive golden-ratio primal–dual algorithm needs no step-size cap—its own adaptive rule keeps step-sizes bounded—and provides two accelerated variants with ergodic 1/N² rates under strong convexity.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-04 04:23 UTC pith:SZLT62NC
load-bearing objection The no-cap step-size result is a genuinely useful fix, and Algorithm 3's acceleration is well proved, but the second accelerated-rate theorem (Algorithm 4) is stated without its proof and relies on a trial-and-error threshold, so the paper needs revision before the abstract's two-variant claim is credible. the 3 major comments →
Two Adaptive Accelerated Golden Ratio Primal--Dual Algorithms With an Application to Poisson Imaging Problem
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
At the center of the paper is a single observation: the artificial upper bound τ_max placed on primal step-sizes in the earlier aEGRPDA is redundant. Writing the update as τ_n = min{ρτ_{n-1}, c_n/τ_{n-1}} with c_n bounded above, the inequality min{a,b} ≤ √(ab) yields τ_n ≤ √(ρ c_n) ≤ U, so the adaptive rule is self-bounding. This leads to Algorithm 2 (PF-GRPDA), a parameter-free method for locally smooth h, with ergodic O(1/N) guarantees for objective residual and feasibility violation and linear convergence when f and g* are strongly convex. The paper then derives two accelerated variants: Algorithm 3, which grows the dual scaling β_n via β_n = β_{n-1}(1 + μζ_n τ_{n-1}) when f is strongly c
What carries the argument
The machinery is the adaptive primal step-size update τ_n = min{ρτ_{n-1}, α_n α_{n-1} ψ θ_{n-1} / ((L_n² + βψ‖K‖²)τ_{n-1})}, where L_n is the local estimate of the Lipschitz constant of ∇h, combined with the golden-ratio convex averaging z_n = (ψ−1)/ψ x_{n-1} + 1/ψ z_{n-1} with ψ∈(1,φ]. The critical handle is Lemma 2.5: min{a,b} ≤ √(ab), applied to the two branches of the update, which yields the uniform bound τ_n ≤ U independent of all iterates. For the accelerated variants, the dual-primal ratio β_n is made to grow (β_n = β_{n-1}(1+μζ_n τ_{n-1}) for strong convexity of f, β_n = β_{n-1}(1+γτ_{n-1}) for strong convexity of h); the proofs show β_n grows quadratically, so the weighted ergodic
Load-bearing premise
The accelerated 1/N² rate for the h-strongly-convex variant (Algorithm 4) is only proved if the acceleration parameter γ stays below a threshold built from the global strong-convexity constant µ_h of h; if µ_h is unknown or misestimated, or γ is chosen above the threshold, the telescoping inequality that yields the rate does not follow.
What would settle it
Run Algorithm 2 on the quadratic test in Section 3 with no τ_max and record the primal step-sizes: for every n the bound τ_n ≤ √(ρ c_max) from Remark 4.2 must hold, and the iterates must converge; any τ_n exceeding that bound, or any divergence, refutes the parameter-free claim.
If this is right
- Users can drop the τ_max hyperparameter: the ergodic O(1/N) rates for objective residual and feasibility violation hold with no step-size cap.
- When f and g* are both strongly convex, Algorithm 2 converges linearly, giving a linearly convergent, locally-smooth primal–dual method with no external tuning except β, ψ, α.
- With f strongly convex, Algorithm 3 obtains an ergodic O(1/N²) rate while keeping h only locally smooth and needing no linesearch or global Lipschitz constant.
- With h globally strongly convex, Algorithm 4 obtains the same O(1/N²) ergodic rate under a step-size rule that remains adaptive.
- On Poisson imaging problems, the accelerated variants reduce feasibility violation and objective residual faster than the base method in the reported runs.
Where Pith is reading between the lines
- The min-of-two-branches bounding trick likely extends to other adaptive first-order methods: any step-size update that combines a multiplicative growth branch with a reciprocal local-curvature branch is automatically bounded without a cap.
- The two acceleration mechanisms are complementary and depend on how the problem is split: placing strong convexity in f or in h determines which accelerated variant applies, so the splitting choice itself becomes an algorithmic lever.
- The threshold γ̄ for Algorithm 4 depends on the global strong-convexity constant µ_h; estimating µ_h adaptively along the iterates would complete the parameter-free story, and the paper explicitly lists this as an open direction.
- The heuristic adaptive-β rule used in the experiments is outside the proved theory; a convergence proof for it would extend the parameter-free guarantee to the primal–dual scaling ratio.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies a class of adaptive golden-ratio primal–dual methods for composite convex optimization (1), where the differentiable term h is only locally smooth. It first revisits the aEGRPDA algorithm of Soe et al. [26] and removes the artificial step-size cap τ_max. The key structural argument is Remark 4.2, which uses Lemma 2.5 (min{a,b} ≤ √(ab)) to show that the adaptive rule (13) itself yields a uniform upper bound on τ_n, so no linesearch, no global Lipschitz constant, and no cap are needed. Algorithms 2, 3, and 4 are then analyzed: Algorithm 2 is shown to have ergodic O(1/N) objective and feasibility rates (Theorem 4.2), and linear convergence under strong convexity of f and g* (Theorem 5.1). Algorithm 3, which exploits strong convexity of f, is proved to have ergodic O(1/N²) rates (Theorem 6.1). Algorithm 4, which exploits global strong convexity of h, is claimed to have the same O(1/N²) rate (Theorem 6.2), but the proof is omitted. Numerical experiments on Poisson imaging problems illustrate the methods in three settings.
Significance. If the results are correct, the paper makes a useful contribution: it provides a principled way to run a golden-ratio primal–dual method without a step-size cap or linesearch under only local smoothness, and it extends accelerated O(1/N²) guarantees to a locally smooth setting, which is uncommon in the literature. The proof that the adaptive rule self-bounds τ_n (Remark 4.2) is simple and elegant, and the resulting O(1/N) estimates that are independent of τ_max genuinely improve on prior work [26]. The linear-convergence section (Section 5) is carefully written, with explicit constants and a clear contraction argument. The main weakness is that the second accelerated result (Theorem 6.2 for Algorithm 4) is stated without proof, and the numerical experiments choose γ via trial and error after computing γ̄ from (63), which depends on the global strong-convexity constant μ_h. This leaves the paper's second central accelerated-rate claim under-supported.
major comments (3)
- [Section 6.1, Theorem 6.2] Theorem 6.2, the O(1/N²) rate for Algorithm 4, is stated without proof: 'The proof follows an analogous argument as in Remark 6.3, Lemma 6.4, Lemma 6.5 and Theorem 6.1. Because of its simplicity, we omit the details.' This is a load-bearing omission. The analogous argument must establish the lower step-size bound τ_n ≥ M̄/√(L²+Cβ_n) with M̄ independent of n, the quadratic growth β_n ≥ c₀n², and β_nτ_n ≥ c₁n for the fixed-γ update (64). None of these steps appears in the text for Algorithm 4, and the presence of γ in (64) changes the recursion substantially from the μ-driven update of Algorithm 3. The rate (56) therefore is not demonstrated for Algorithm 4 as stated.
- [Section 6.1, Eq. (63) and Section 7.1.3] The threshold γ̄ in (63) depends on μ_h, the global strong-convexity constant of h. In the experiments, γ = 0.99 γ̄ is selected only after trial and error (Section 7.1.3: 'after a few trial and error, we are satisfied with β₀ = 5, and after computing γ̄ from (63), select γ = 0.99 ¯γ'). If μ_h is unknown or overestimated, Lemma 6.8's telescoping argument (the inequalities following (72)) may fail: the γτ_n terms would not be absorbed by μ_hτ_n and θ_n terms, so (69) would not telescope and (56) would not follow. The paper does not provide a strategy for estimating μ_h or a robustness analysis for misspecified μ_h. This is connected to the omission of the proof of Theorem 6.2 and should be addressed explicitly.
- [Section 4, Lemma 4.2] Lemma 4.2's lower bound on τ_n and θ_n relies on [37, Lemma 4.2] without reproducing the statement or verifying its hypotheses for Algorithm 2. Since this lower bound is used in Theorem 4.1 and Theorem 4.2 to obtain nonzero Δ and the O(1/N) rate, the dependence should be made transparent: state the lemma or at least explicitly verify the required conditions. The reader should not have to consult a separate paper to see whether the assumptions (e.g., the specific form of the step-size update) match.
minor comments (6)
- [Section 7.1.3, paragraph after Fig. 13] The text refers to 'Algorithm 6' in 'the accelerated method (Algorithm 6) yields a lower overall objective residual'. The algorithm is Algorithm 4. Please correct the numbering.
- [Abstract and Introduction] The phrase 'parameter-free' is used for Algorithm 2, but the method still depends on β, ψ, α_n, and τ₀. What the paper actually shows is that the rate estimates do not depend on an artificial cap τ_max. Please qualify the term, e.g., 'cap-free' or 'parameter-free in the convergence-rate bound'.
- [Section 4, Remark 4.1] The convention '0/0 = +∞' is stated, but the update (13) when x_n = x_{n-1} and L_n = 0 gives a denominator of zero. The convention makes the fraction equal to +∞, so τ_n = min{ρτ_{n-1}, +∞} = ρτ_{n-1}, which is consistent with the remark, but this should be stated more explicitly because the usual computer arithmetic would produce NaN.
- [Section 6, Algorithm 3 and Lemma 6.4] The definition of M̄ in Lemma 6.4 contains τ₁ and τ₂, which are defined by the algorithm. The induction proof then claims the bound for n=1,2 by definition. This is fine, but the notation M̄ is used before τ₁ and τ₂ are introduced as deterministic functions of the input. Suggest moving the induction start to n=3 or clarifying that τ₁,τ₂ are fixed by the initial data.
- [Section 7, general] Figure captions and text frequently write 'PFGRPDA' instead of 'PF-GRPDA'. Also, the caption of Figure 3 says 'Several heuristic adaptive-β n for PFGRPDA' and 'Thin faded curves show individual heuristic choices' – this is a bit confusing because the figure seems to show only one method with several β-update variants. Please clarify.
- [Section 2, Lemma 2.5] Lemma 2.5 is stated as 'min{a,b} ≤ √(ab)' for a,b>0. This is true but unnecessarily weak: the sharpest bound is min{a,b} ≤ √(ab), which is exactly the geometric mean. The proof is fine, but the lemma could be stated as an equality-like bound without overclaiming.
Circularity Check
No significant circularity: the no-cap step-size bound is derived in-line from the adaptive update, not assumed. The only caveats are a non-load-bearing self-citation to [26] and an omitted proof for the second accelerated rate, which is a completeness risk rather than a circular step.
full rationale
The central no-cap claim is self-contained. In Remark 4.2 the paper rewrites update (13) as tau_n = min(rho tau_{n-1}, c_n / tau_{n-1}), applies Lemma 2.5 (min{a,b} <= sqrt(ab), proved in the paper) to obtain tau_n <= sqrt(rho c_n), and then bounds c_n using theta_n <= 1+1/psi and D_n >= beta psi ||K||^2, giving tau_n <= U = sqrt(rho c_max). This is a direct algebraic consequence of the step-size rule, not an input equivalent to the conclusion. The lower bound in Lemma 4.2 cites [37, Lemma 4.2], an external lemma by Tam--Uteda rather than the present authors, and the boundedness needed for it is established in the same lemma from inequality (17); even if that citation were questioned, it would not make the upper-bound result circular. The self-citation to [26] supplies the base aEGRPDA and the previous constant C1, but the new proof does not use [26] to justify removal of tau_max, so it is not load-bearing. The O(1/N^2) rate for Algorithm 3 is fully proved, while Theorem 6.2 for Algorithm 4 is asserted with "we omit the details" (Section 6.1), and the gamma threshold (63) requires the strong-convexity constant mu_h, with gamma = 0.99 gamma_bar selected by trial and error in Section 7.1.3. These are completeness and parameter-sensitivity risks, not circular steps: no rate constant is fitted to data, and the theorem is conditional on the stated gamma bound. No prediction reduces by construction to a fitted value.
Axiom & Free-Parameter Ledger
free parameters (5)
- beta (Algorithm 2) / beta0 (Algorithms 3,4)
- psi =
1.61 in Algorithm 4 experiments
- alpha_n / alpha
- tau0 =
0.30U in Algorithm 4 experiments
- gamma (Algorithm 4) =
0.99 gamma-bar
axioms (6)
- domain assumption Assumption 2.1: saddle point of (3) exists and prox of f,g are computable
- domain assumption Assumption 4.1: f,g proper convex lsc; h convex and locally smooth
- domain assumption Assumption 5.1: f is mu_f-strongly convex and g* is mu_g*-strongly convex
- domain assumption Assumption 6.1: f is mu-strongly convex
- domain assumption Assumption 6.2: h is globally mu_h-strongly convex and locally smooth
- standard math [37, Lemma 4.2] lower bound on tau_n for adaptive step sizes
read the original abstract
This paper revisits the adaptive extended golden-ratio primal--dual algorithm (aEGRPDA) proposed by Soe et al. (2026) for structured convex optimisation problems involving a differentiable term that is only locally smooth. We prove that the artificial upper bound imposed on the primal step-size in aEGRPDA is redundant, since the adaptive rule itself keeps the step-sizes bounded above. As a consequence, the ergodic $\mathcal O(1/N)$ estimates for the objective residual and feasibility violation, where $N\ge1$ denotes the number of iterations, are independent of this hyperparameter. Consequently, the resulting adaptive golden-ratio primal--dual method, therefore, requires neither a step-size cap, nor a linesearch procedure, nor a known global Lipschitz constant. We establish linear convergence of the algorithm when both the primal and dual functions are strongly convex. Furthermore, we develop two accelerated variants, in addition to the local smoothness assumption: one for the case where the nonsmooth primal component is strongly convex, and another for the case where the differentiable term is globally strongly convex. For these accelerated methods, we prove an ergodic $\mathcal O(1/N^2)$ convergence rate. Preliminary numerical experiments on a Poisson imaging problem illustrate the efficiency and robustness of the proposed approaches.
Reference graph
Works this paper leans on
-
[1]
Chambolle, A., Pock, T.: A first-order primal-dual algorithm for convex problems with applications to imaging. J. Math. Imaging Vision40, 120–145 (2011)
2011
-
[2]
Signal Processing: Image Communication117, 117012 (2023)
Chen, M., Wen, M., Tang, Y.: First-order primal–dual algorithm for image restoration corrupted by mixed Poisson–Gaussian noise. Signal Processing: Image Communication117, 117012 (2023)
2023
-
[3]
Fixed Point Theory Appl.2016, 1–18 (2016)
Chen, P., Huang, J., Zhang, X.: A primal-dual fixed point algorithm for minimization of the sum of three convex separable functions. Fixed Point Theory Appl.2016, 1–18 (2016)
2016
-
[4]
Set-Valued Var
Combettes, P.L., Pesquet, J.-C.: Primal-dual splitting algorithm for solving inclusions with mixtures of composite, Lipschitzian, and parallel-sum type monotone operators. Set-Valued Var. Anal.20(2), 307–330 (2012)
2012
-
[5]
Esser, E., Zhang, X., Chan, T.F.: A general framework for a class of first order primal-dual algorithms for convex optimization in imaging science. SIAM J. Imaging Sci.3(4), 1015–1046 (2010)
2010
-
[6]
IEEE Signal Process
Pan, Z., Liu, Z., Luo, K., Zhao, Y., Xu, X.: Compressive sensing total-variation primal-dual algorithms for image reconstruction. IEEE Signal Process. Lett (2024)
2024
-
[7]
Acta Math
Tang, Y.C., Zhu, C.X., Wen, M., Peng, J.G.: A splitting primal-dual proximity algorithm for solving composite optimization problems. Acta Math. Sin. Engl. Ser.33(6), 868–886 (2017)
2017
-
[8]
Vladarean, M.L., Malitsky, Y., Cevher, V.: A first-order primal-dual method with adaptivity to local smoothness. Adv. Neural Inf. Process. Syst.34, 6171–6182 (2021)
2021
-
[9]
SIAM, Philadelphia (2017)
Beck, A.: First-order Methods in Optimization. SIAM, Philadelphia (2017)
2017
-
[10]
Princeton University Press, Princeton (1970)
Rockafellar, R.T.: Convex Analysis. Princeton University Press, Princeton (1970)
1970
-
[11]
Chang, X., Yang, J.: GRPDA revisited: Relaxed condition and connection to Chambolle-Pock’s primal- dual algorithm. J. Sci. Comput.93(3), 70 (2022)
2022
-
[12]
Zhou, D., Chang, X., Yang, J.,et al.: A new primal-dual algorithm for structured convex optimization involving a Lipschitzian term. Pac. J. Optim.18(2), 497–517 (2022)
2022
-
[13]
Springer, New York (2017)
Bauschke, H.H., Combettes, P.L.: Convex Analysis and Monotone Operator Theory in Hilbert Spaces. Springer, New York (2017)
2017
-
[14]
In: 2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp
Jezierska, A., Chouzenoux, E., Pesquet, J.-C., Talbot, H.: A primal-dual proximal splitting approach for restoring data corrupted with Poisson-Gaussian noise. In: 2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), pp. 1085–1088 (2012). IEEE 31
2012
-
[15]
In: 2018 European Control Conference (ECC), pp
Latafat, P., Bemporad, A., Patrinos, P.: Plug and play distributed model predictive control with dynamic coupling: A randomized primal-dual proximal algorithm. In: 2018 European Control Conference (ECC), pp. 1160–1165 (2018). IEEE
2018
-
[16]
Chang, X., Yang, J.: A golden ratio primal–dual algorithm for structured convex optimization. J. Sci. Comput.87, 1–26 (2021)
2021
-
[17]
Malitsky, Y., Pock, T.: A first-order primal-dual algorithm with linesearch. SIAM J. Optim.28(1), 411–432 (2018)
2018
-
[18]
IEEE Signal Process
Komodakis, N., Pesquet, J.-C.: Playing with duality: An overview of recent primal? dual approaches for solving large-scale optimization problems. IEEE Signal Process. Mag.32(6), 31–54 (2015)
2015
-
[19]
Condat, L.: A primal–dual splitting method for convex optimization involving Lipschitzian, proximable and linear composite terms. J. Optim. Theory Appl.158(2), 460–479 (2013)
2013
-
[20]
Chambolle, A., Pock, T.: On the ergodic convergence rates of a first-order primal–dual algorithm. Math. Program.159(1), 253–287 (2016)
2016
-
[21]
V˜ u, B.C.: A splitting algorithm for dual monotone inclusions involving cocoercive operators. Adv. Comput. Math.38(3), 667–681 (2013)
2013
-
[22]
Yan, M.: A new primal–dual algorithm for minimizing the sum of three functions with a linear operator. J. Sci. Comput.76, 1698–1717 (2018)
2018
-
[23]
Salim, A., Condat, L., Mishchenko, K., Richt´ arik, P.: Dualize, split, randomize: Toward fast nonsmooth optimization algorithms. J. Optim. Theory Appl.195(1), 102–130 (2022)
2022
-
[24]
Malitsky, Y., Tam, M.K.: A first-order algorithm for decentralised min-max problems. Numer. Math. 158(3), 1187–1206 (2026)
2026
-
[25]
Malitsky, Y.: Golden ratio algorithms for variational inequalities. Math. Program.184(1-2), 383–410 (2020)
2020
-
[26]
Soe, S., Tam, M.K., Vetrivel, V.: The golden ratio primal-dual algorithm with two new stepsize rules for convex-concave saddle point problems. Comput. Optim. Appl.93(3), 1355–1399 (2026)
2026
-
[27]
arXiv preprint arXiv:2301.04431v4 (2023)
Latafat, P., Themelis, A., Stella, L., Patrinos, P.: Adaptive proximal algorithms for convex optimiza- tion under local Lipschitz continuity of the gradient. arXiv preprint arXiv:2301.04431v4 (2023)
Pith/arXiv arXiv 2023
-
[28]
Di Serafino, D., Landi, G., Viola, M.: ACQUIRE: an inexact iteratively reweighted norm approach for TV-based Poisson image restoration. Appl. Math. Comput.364, 124678 (2020)
2020
-
[29]
Bauschke, H.H., Bolte, J., Teboulle, M.: A descent lemma beyond Lipschitz gradient continuity: first- order methods revisited and applications. Math. Oper. Res.42(2), 330–348 (2017)
2017
-
[30]
Driggs, D., Ehrhardt, M.J., Sch¨ onlieb, C.-B., Tang, J.: Practical acceleration of the Condat–V˜ u algorithm. SIAM J. Imaging Sci.17(4), 2076–2109 (2024)
2076
-
[31]
arXiv preprint arXiv:1706.02602, 3 (2017)
Malitsky, Y.: Chambolle-pock and Tseng’s methods: relationship and extension to the bilevel optimization. arXiv preprint arXiv:1706.02602, 3 (2017)
Pith/arXiv arXiv 2017
-
[32]
Chen, Y., Lan, G., Ouyang, Y.: Optimal primal-dual methods for a class of saddle point problems. SIAM J. Optim.24(4), 1779–1814 (2014)
2014
-
[33]
Nesterov, Y.: Gradient methods for minimizing composite functions. Math. Program.140(1), 125–161 (2013)
2013
-
[34]
Nesterov, Y.: Introductory Lectures on Convex Optimization: A Basic Course vol. 87. Springer, New York, NY (2013). https://doi.org/10.1007/978-1-4419-8853-9
-
[35]
arXiv preprint arXiv:2604.09245 (2026)
Condat, L., Sadiev, A., Richt´ arik, P.: A Nesterov-accelerated primal-dual splitting algorithm for 32 convex nonsmooth optimization. arXiv preprint arXiv:2604.09245 (2026)
Pith/arXiv arXiv 2026
-
[36]
Chang, X., Yang, J., Zhang, H.: A convex combination based primal-dual algorithm with linesearch for general convex-concave saddle point problems. IMA J. Numer. Anal., 158 (2026)
2026
-
[37]
Tam, M.K., Uteda, D.J.: Bregman golden ratio algorithms for variational inequalities. J. Optim. Theory Appl.199(3), 993–1021 (2023)
2023
-
[38]
Chang, X.-K., Yang, J., Zhang, H.: Golden ratio primal-dual algorithm with linesearch. SIAM J. Optim.32(3), 1584–1613 (2022)
2022
-
[39]
Sun, D., Toh, K.-C., Yang, L.: A convergent 3-block semiproximal alternating direction method of multipliers for conic programming with 4-type constraints. SIAM J. Optim.25(2), 882–915 (2015)
2015
-
[40]
Soe, S., Vetrivel, V.: The golden ratio proximal admm with norm independent step-sizes for separable convex optimization. J. Optim. Theory Appl.210(1), 18 (2026)
2026
-
[41]
Yin, C., Yang, J.: Golden ratio proximal gradient admm for distributed composite convex optimization. J. Optim. Theory Appl.200(3), 895–922 (2024) 33
2024
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.