REVIEW 2 major objections 5 minor 23 references
Strong convergence and fast rates for systems with Tikhonov regularization
T0 review · 2 major / 5 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read For a monotone equation Ax=0 in a Hilbert space, the paper proves that a second-order Tikhonov-regularized dynamics converges strongly to the minimal-norm solution at rates close to those of unregularized accelerated flows.
desk verdict The new system is worth attention, but the main proof has a missing β in the discriminant analysis that breaks the negativity step for αβ≤1. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying object is the energy functional $E(t)$, a Lyapunov function whose main ingredients are $v(t)=\frac{1}{2}\|b(x(t)-x_t)+t^q(2\dot{x}(t)+\beta t^q A(x(t)))\|^2$, a monotonicity term $u(t)$ built from $\langle A(x(t)),x(t)-x_t\rangle$, and weighted squared norms of $A(x(t))$, $x(t)$, and $x(t)-x_t$. Differentiating $E(t)$ along solutions of (DS) produces a differential inequality of the form $\dot{E}(t)+\frac{K}{t^{q+s}}E(t)\le C t^{q+s-2}+C t^{-q-2s}-\frac{d}{dt}(\cdot)$, and the algebraic core of the proof is choosing auxiliary constants so that the quadratic form in $\|\dot{x}\|^2$, $\langle A,\dot{x}\rangle$, and $\|A\|^2$ is negative for large $t$. The Tikhonov path $x_t$, the unique zero of $A+\frac{c}{t^{2q+s}}\mathrm{Id}$, is what carries the strong convergence toward the minimal-norm solution.
What would settle it
Take $A(x,y)=(-y,x)$ on $\mathbb{R}^2$, a monotone Lipschitz, non-cocoercive operator whose only zero is the origin, fix parameters such as $\alpha=2$, $q=0.5$, $s=0.25$, $\beta=1$, $\gamma=1$, and $c$ below the stated bound, and integrate (DS) from different initial conditions; if $\|(x(t),y(t))\|$ does not decay as $O(t^{q+s-1})+O(t^{-s/2})$ or $\|A(x(t))\|$ does not match the stated rate, Theorem 1 fails. Alternatively, exhibiting a monotone continuous operator for which no strong global solution of (DS) exists would falsify the regularity premise under which the rates are derived.
Extended reading notes
Core claim
The central assertion is Theorem 1: for parameters $\alpha>1$, $q,\beta,\gamma,s,c>0$ with $0<q+s<1$ and $c<\frac{8\alpha(\alpha-1)\gamma}{\alpha^2\beta^2+8(\alpha-1)\beta}$, every trajectory of the system (DS) satisfies $\|x(t)-x_t\|=O(t^{q+s-1})+O(t^{-s/2})$, and consequently $x(t)\to x^*$ strongly as $t\to+\infty$, where $x_t$ is the unique zero of $A+\frac{c}{t^{2q+s}}\mathrm{Id}$ and $x^*$ is the projection of $0$ onto the zero set of $A$. The proof constructs a Lyapunov functional $E(t)$ built from the velocity, the operator value, and the distance to the Tikhonov path $x_t$, and it shows that along the trajectory $\dot{E}(t)+\frac{K}{t^{q+s}}E(t)$ is bounded by integrable remainder terms. Integrating this differential inequality yields the stated rates for $\|A(x(t))\|$ and $\|\dot{x}(t)\|$. Because the dynamics evaluates $A$ in a forward way rather than through a resolvent, it is directly implementable whenever the operator can be evaluated along a trajectory.
Load-bearing premise
The proof needs the trajectory $x(t)$ to exist for all $t\ge t_0$ with $t\mapsto A(x(t))$ absolutely continuous, but the paper only guarantees such a strong global solution when $A$ is Lipschitz continuous, while the abstract and theorem state the weaker hypothesis that $A$ is monotone and continuous. If a monotone continuous but non-Lipschitz operator does not admit such a solution, the claimed rates have no trajectory to apply to.
Editorial extensions
If this is right
- Choosing $s=\frac{2(1-q)}{3}$ gives $\|\dot{x}(t)\|=O(t^{-(1+2q)/3})$ and $\|A(x(t))\|=O(t^{-(1+5q)/3})$; for $q$ close to $1$ these approach the rates $O(t^{-1})$ and $O(t^{-1-q})$ of the unregularized system in [15].
- For the primal-dual system (34), both the primal trajectory $x(t)$ and the dual trajectory $y(t)$ converge strongly to the minimal-norm saddle point, with $\|Bx(t)-b\|$ and $|f(x(t))-f(x^*)|$ decaying at the orders stated in Theorem 2.
- Because the dynamics uses forward evaluations of $A$ instead of resolvent-based regularizations, it offers a tractable continuous-time model for monotone inclusions where cocoercivity fails, such as saddle-point and skew-operator problems.
- The Tikhonov term acts as a selection device: irrespective of the starting point, the strong limit is always the projection of $0$ onto the zero set of $A$, the minimal-norm solution.
Reading between the lines
- Extension: the same Tikhonov-plus-Newton structure could be discretized into an algorithm with variable step sizes; the continuous rates suggest iterate convergence at similar orders, but the correction term $\beta t^q\frac{d}{dt}A(x(t))$ would require numerical differentiation or a discrete analogue.
- Testable prediction: for a monotone affine map $A(x)=Mx$ with symmetric positive semidefinite $M$, the theorem predicts that the trajectory approaches the projection of $0$ onto $\ker M$ at exactly the stated rates; this case can be solved in closed form and checked numerically.
- Connection: in saddle-point problems, weak convergence alone leaves the limit ambiguous, so the strong convergence to the minimal-norm saddle point gives a principled selection mechanism that could be transferred to discrete primal-dual algorithms.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript studies the second-order dynamical system (DS) with vanishing damping α/t^q, a Newton-type correction βt^q (d/dt)A(x(t)), and Tikhonov regularization (c/t^{2q+s})x(t) for a monotone equation Ax=0 on a Hilbert space. The main result (Theorem 1) claims that, for α>1 and 0<q+s<1, the trajectory satisfies ||x(t)-x_t||=O(t^{q+s-1})+O(t^{-s/2}), whence it converges strongly to the minimal-norm solution, together with rates for ||A(x(t))|| and ||ẋ(t)||. Section 3 applies this to a primal-dual system for linearly constrained convex optimization, obtaining strong convergence and rates for the feasibility measure and objective values. The proof is based on a Lyapunov functional with coefficients analyzed through asymptotic expansions.
Significance. If the central estimate is correct, the paper provides a forward-evaluated Newton-like monotone dynamics with strong convergence to the minimal-norm solution of a monotone inclusion, at rates close to the known accelerated rates for systems without Tikhonov regularization. The Lyapunov construction is explicit and the coefficient analysis is largely detailed; in particular, the proof does not rely on fitted constants or on a conclusion that is equivalent to an input assumption. The application to linearly constrained convex optimization is natural and the derived rates would be a useful addition to the literature. However, the proof contains a sign-error in the discriminant calculation that invalidates the key negativity step for a substantial parameter region, so the main theorem is not established as stated.
major comments (2)
- [§2, Eq. (26)] The displayed leading coefficient of R2^2−4R1R3 omits the factor β that is present in R3(t) in (25). With R3(t) = β(−2+s1+bs4+K s6 b/2)t^{3q}+O(t^{3q−s}), the correct leading coefficient is D0 = ((2b−2α)β−4)^2 −4β(2b+s3b+s5b−4α)(−2+s1+bs4+K s6 b/2). Setting b=α and s1=s3=s4=s6=0 gives D0=16(1−αβ)+8αβs5, which is strictly positive for αβ≤1 and every allowed s5>0. More generally, if R1<0 then u=2−s3−s5>0 and, writing w=s1+αs4+Kαs6/2>0, one has D0=16−4αβu(2−w); since u<2 and 2−w<2, this is positive whenever αβ≤1. Thus for β≤1/α, a parameter region allowed by Theorem 1, the negativity criterion leading to (30) cannot hold. The missing factor is therefore not a harmless typo: it changes the sign of the discriminant as β varies. Please correct (26), add a lower bound on β (for example β>1/α) if that is the intended parameter regime, and restate Theorem 1 and Theorem 2 accordingly, or provide an alternative argument covering all stated parameters.
- [§2, Theorem 1 and preceding paragraph] The theorem is stated for a monotone continuous operator A, but the system (DS) contains the term βt^q (d/dt)A(x(t)). The paragraph before Theorem 1 guarantees existence of a strong global solution only when A is Lipschitz (citing [15]), and the proof additionally requires t↦A(x(t)) to be absolutely continuous. As written, the hypotheses of Theorem 1 do not ensure that there is any trajectory generated by (DS) satisfying the regularity used in the proof. Please either include the Lipschitz or other sufficient regularity condition in the statement of Theorem 1, or formulate the result conditionally for any strong global solution with the stated absolute-continuity property, and adjust the abstract so that the claimed scope matches the hypotheses.
minor comments (5)
- [§2, below Eq. (16)] The phrase 'for every s1, s2, s3.s4 > 0' contains a typo; it should read 's1, s2, s3, s4'.
- [Abstract and Remark 3] The phrase 'very closed to' should be 'very close to'; there is also an editorial spacing error in 'traj ectories' in the abstract.
- [§2, Eq. (32)] The negative term −(bβT^{-s}/2)||x_T||^2 is dropped without comment when passing to the final estimate; since the term is nonpositive the inequality is valid, but stating this would improve clarity.
- [§2, Eq. (31)] The auxiliary inequality 't^u e^{W t^v} ≤ C d/dt( t^{u−v+1} e^{W t^v} )' is asserted without proof; a one-line verification or a reference would help the reader check the subsequent integration step.
- [§1 and §2] The sentence 'the starting time in (DS) is t0 > 0' appears twice with the same wording; one occurrence should be removed.
Circularity Check
No circularity: the Lyapunov derivation is self-contained; cited prior results are auxiliary lemmas.
full rationale
The central proof of Theorem 1 is a direct Lyapunov estimate. The energy functional E(t) is explicitly built from the trajectory of (DS) and the monotonicity of A, and the chain of inequalities (5)-(29) consists of algebraic manipulations and Young-type estimates with auxiliary constants s1-s6 and K. The negativity of the quadratic form (R1,R2,R3) and the sign conditions on R4-R6 are derived from explicit leading-order formulas, not assumed or fitted from the conclusion. Inequality (30), after multiplication by the exponential weight and integration, yields E(T) ≤ C0 T^{2q+2s-2}+C0T^{-s}; the rates for ||x-x_t||, ||A(x)||, and ||ẋ|| then follow from the definition of E(t). No step invokes Theorem 1 or the desired strong-convergence statement as an input. The Tikhonov path x_t is used only through standard facts recalled from [14] (strong convergence to x*, ||x_t|| ≤ ||x*||, and ||d/dt x_t|| ≤ (p/t)||x_t||); these are stated auxiliary lemmas whose hypotheses do not include the target rates and they are not equivalent to the theorem. The self-citation to [15] concerns existence/uniqueness under a Lipschitz assumption, a regularity premise rather than the convergence claim. There are no fitted parameters renamed as predictions and no self-citation chain that forces the choice of the system. The skeptic's β-factor concern about the discriminant in Eq. (26) is a possible algebraic correctness gap in proving R2^2-4R1R3<0; even if valid, it is a gap in the justification of sign negativity, not a circular dependency, so it does not affect the circularity score.
Assumptions & free parameters
free parameters (1)
- Auxiliary Lyapunov constants b, K, s1 through s6 =
b=alpha; K<min(2theta/(4+alpha*beta),2c/(3alpha)); s_i small positive
assumptions (5)
- domain assumption Existence and uniqueness of a strong global solution of (DS) when A is Lipschitz continuous and monotone.
- domain assumption Tikhonov path theory: for monotone A, the zero x_epsilon of A+epsilon Id converges strongly to the minimal-norm solution and satisfies the derivative bound in equations (3) and (4).
- domain assumption The operator A is monotone and continuous on a real Hilbert space, and its zero set is nonempty.
- domain assumption In the application, f is C2 convex and B is a continuous linear operator with b in the strong relative interior of B(H), so that the KKT conditions characterize solutions.
- standard math Standard inequalities (Young, Cauchy-Schwarz) and exponential integration arguments used in the Lyapunov analysis.
Cite this review
Pith. "Pith review of Strong convergence and fast rates for systems with Tikhonov regularization." pith.science (2026). https://pith.science/paper/73OUTTT6
@misc{pith2026241117329,
author = {Pith},
title = {Pith review of: Strong convergence and fast rates for systems with Tikhonov regularization},
year = {2026},
howpublished = {\url{https://pith.science/paper/73OUTTT6}},
note = {Machine review of arXiv:2411.17329}
}
read the original abstract
We introduce and investigate the asymptotic behaviour of the trajectories of a second order dynamical system with Tikhonov regularization for solving a monotone equation with single valued, monotone and continuous operator acting on a real Hilbert space. We consider a vanishing damping which is correlated with the Tikhonov parameter and which is in line with recent developments in the literature on this topic. A correction term which involves the time derivative of the operator along the trajectory is also involved in the system and makes the link with Newton and Levenberg-Marquardt type methods. We obtain strong convergence of the trajectory to the minimal norm solution and fast convergence rates for the velocity and a quantity involving the operator along the trajectory. The rates are very closed to the known fast convergence results for systems without Tikhonov regularization, the novelty with respect to this is that we also obtain strong convergence of the trajectory to the minimal norm solution. As an application we introduce a primal-dual dynamical system for solving linearly constrained convex optimization problems, where the strong convergence of the trajectories is highlighted together with fast convergence rates for the feasibility measure and function values.
Reference graph
Works this paper leans on
-
[15]
R.I. Bot ¸, E.R. Csetnek, D.K. Nguyen, Fast Optimistic Gradient Descent Ascent (OGDA) Method in Continuous and Discrete Time , Found Comput Math 2023, https://doi.org/10.1007/s10208-023 -09636-5
-
[1]
V. Apidopoulos, J.-F. Aujol, Ch. Dossal, The differential inclusion modeling the FISTA algorithm and optimality of convergence rate in the case b ≤ 3, SIAM J. Optim. 28(1) (2018), 551—574
work page 2018
-
[2]
H. Attouch, Z. Chbani, J. Peypouquet, P. Redont, Fast convergence of inertial dynamics and algorithms with asymptotic vanishing viscosity , Mathematical Programming 168 (1-2) (2018), 123–175
work page 2018
-
[3]
H. Attouch, Z. Chbani, H. Riahi, Combining fast inertial dynamics for convex optimization w ith Tikhonov regularization, J. Math. Anal. Appl 457 (2018), 1065–1094
work page 2018
-
[4]
H. Attouch, S. L´ aszl´ o,Convex optimization via inertial algorithms with vanishin g Tikhonov regularization: fast convergence to the minimum norm solution , Math Meth Oper Res 99, 307–347 (2024)
work page 2024
-
[5]
C.D. Alecsa, S.C. L´ aszl´ o, Tikhonov Regularization of a Perturbed Heavy Ball System wi th Vanishing Damping, SIAM Journal on Optimization, 31(4), 2921-2954, 2021
work page 2021
-
[6]
C.D. Alecsa, S.C. L´ aszl´ o, T. Pint ¸a,An Extension of the Second Order Dynamical System that Model s Nesterov’s Convex Gradient Method , Applied Mathematics and Optimization, 84, 1687-1716, 2021
work page 2021
-
[7]
H. Attouch, S.C. L´ aszl´ o,Continuous Newton-like Inertial Dynamics for Monotone Inc lusions, Set-Valued Var. Anal 29, 555–581 (2021)
work page 2021
Show all 23 references
-
[8]
Attouch, J
H. Attouch, J. Peypouquet, Convergence of inertial dynamics and proximal algorithms g overned by max- imal monotone operators , Mathematical Programming 174(1-2), 391-432 (2019)
2019
-
[9]
Attouch, J
H. Attouch, J. Peypouquet, P. Redont, Fast convex optimization via inertial dynamics with Hessia n driven damping, J. Differ. Equ. 261(10), 5734–5783 (2016)
2016
-
[10]
Attouch, A
H. Attouch, A. Balhag, Z. Chbani, H. Riahi, Damped inertial dynamics with vanishing Tikhonov regu- larization: Strong asymptotic convergence towards the min imum norm solution , Journal of Differential Equations 311, 29-58 (2022)
2022
-
[11]
CMS Books in Mathematics
Bauschke, H., Combettes, P.L.: Convex Analysis and Monotone O perator Theory in Hilbert spaces. CMS Books in Mathematics. Springer (2011)
2011
-
[12]
Bot ¸, E.R
R.I. Bot ¸, E.R. Csetnek, S.C. L´ aszl´ o,Tikhonov regularization of a second order dynamical system with Hessian damping , Math. Program. 189 (2021), 151–186
2021
-
[13]
Bot ¸, E.R
R.I. Bot ¸, E.R. Csetnek, S.C. L´ aszl´ o,A second order dynamical approach with variable damping to n oncon- vex smooth minimization , Applicable Analysis (2018). https://doi.org/10.1080/00036811.20 18.1495330
2018 doi
-
[14]
Bot ¸, E.R
R.I. Bot ¸, E.R. Csetnek, S.C. L´ aszl´ o,On the strong convergence of continuous Newton-like inerti al dynamics with Tikhonov regularization for monotone inclusions , Journal of Mathematical Analysis and Applications, 530(2), 2024
2024
-
[16]
R. I. Bot ¸, D.-K. Nguyen, Improved convergence rates and trajectory convergence for primal-dual dynamical systems with vanishing damping , Journal of Differential Equations 303, 369-406, 2021 13
2021
-
[17]
R. I. Bot ¸, D.-K. Nguyen, Tikhonov regularization of monotone operator flows not only en- sures strong convergence of the trajectories but also speed s up the vanishing of the residuals , https://arxiv.org/abs/2406.00852, (2024)
2024 arXiv
-
[18]
Karapetyants, S.C
M. Karapetyants, S.C. L´ aszl´ o,A Nesterov type algorithm with double Tikhonov regularizat ion: fast con- vergence of the function values and strong convergence to th e minimal norm solution , Appl Math Optim 90, 17 (2024)
2024
-
[19]
S.C. L´ aszl´ o,On the strong convergence of the trajectories of a Tikhonov r egularized second order dynamical system with asymptotically vanishing damping , Journal of Differential Equations 362, 355-381 (2023)
2023
-
[20]
L´ aszl´ o,Solving convex optimization problems via a second order dyn amical system with implicit Hes- sian damping and Tikhonov regularization , Comput Optim Appl (2024)
S.C. L´ aszl´ o,Solving convex optimization problems via a second order dyn amical system with implicit Hes- sian damping and Tikhonov regularization , Comput Optim Appl (2024). https://doi.org/10.1007/s10589- 024-00620-5
2024 doi
-
[21]
L´ aszl´ o,On the convergence of an inertial proximal algorithm with a T ikhonov regularization term , https://arxiv.org/abs/2302.02115 (2023)
S.C. L´ aszl´ o,On the convergence of an inertial proximal algorithm with a T ikhonov regularization term , https://arxiv.org/abs/2302.02115 (2023)
2023 arXiv
-
[22]
L´ aszl´ o,A proximal-gradient inertial algorithm with Tikhonov regu larization: strong convergence to the minimal norm solution , arXiv:2407.10350 (2024)
S.C. L´ aszl´ o,A proximal-gradient inertial algorithm with Tikhonov regu larization: strong convergence to the minimal norm solution , arXiv:2407.10350 (2024)
2024 arXiv
-
[23]
W. Su, S. Boyd, E. J. Cand ` es, A Differential Equation for Modeling Nesterov’s Accelerate d Gra- dient Method: Theory and Insights , Journal of Machine Learning Research 17(153) (2016), 1-43. N IPS, December 2014. 14
2016
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