REVIEW 2 major objections 4 minor 1 cited by
First-order methods for stochastic and finite-sum convex optimization with deterministic constraints
T0 review · 2 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read Stochastic solutions can meet hard constraints surely at no extra cost
desk verdict A genuinely useful strengthening of the feasibility guarantee, with careful proofs; the infinite-sample result is conditional on a strong uniform gradient bound, and the numerical section is light. 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 load-bearing object is the quadratic penalty subproblem $F_\rho(x)=F(x)+\tfrac{\rho}{2}\|[c(x)]_+\|^2$ together with Lemma 1's bound $\|[c(x)]_+\| \le 2\Lambda/\rho + \sqrt{2(F_\rho(x)-F^*_\rho)/\rho}$. This inequality shows that controlling the penalty suboptimality $F_\rho(x)-F^*_\rho$ and choosing a large enough $\rho$ yields a deterministic bound on the original constraint violation, and the paper selects $\rho$ as a power of the horizon $K$ so that the two terms balance. Algorithm 1 applies an accelerated stochastic gradient scheme once to a sequence of these penalty problems, while Algorithm 2 runs a modified variance-reduced accelerated scheme in which the stochastic estimator approximates only the finite-sum objective and the penalty gradient is computed exactly, keeping the noise confined to the objective component.
What would settle it
Run Algorithm 1 on a constrained stochastic convex problem satisfying all assumptions except the uniform bound $\max_{\xi\in\Xi}\|\nabla\tilde f(x,\xi)\|\le G$, for example $\tilde f(x,\xi)=\xi^\top x$ with $\xi$ standard normal so the stochastic gradient is unbounded, and check whether $\|[c(x_K)]_+\|\le\epsilon$ holds with probability one at the claimed $O(\epsilon^{-2})$ gradient budget; a single output with positive-probability violation above $\epsilon$ falsifies the SFSO claim.
Extended reading notes
Core claim
The paper establishes that an $\epsilon$-surely feasible stochastic optimal ($\epsilon$-SFSO) solution, meaning a point $x$ with $\|[c(x)]_+\| \le \epsilon$ and $E[|F(x)-F^*|] \le \epsilon$, can be computed by a single loop of accelerated stochastic gradient steps applied to the quadratic penalty problems $F_\rho(x)=E[\tilde f(x,\xi)]+\psi(x)+\tfrac{\rho}{2}\|[c(x)]_+\|^2$ with suitably chosen penalty parameters $\rho$. For infinite sample spaces, Algorithm 1 achieves first-order oracle complexity $O(\epsilon^{-2})$ with constant penalty $\rho=K^{3/2}$ and $\tilde O(\epsilon^{-2})$ with dynamic penalties, where the oracle counts gradient evaluations during a single pass. For finite sums of size $s$, Algorithm 2 uses a variance-reduced estimator for the average of the $f_i$ and an exact gradient for the penalty term, and under $m=O(1)$ finds an $\epsilon$-SFSO solution in $O(s\log s + \sqrt{s}\,\epsilon^{-3/2})$ gradient evaluations, with the weaker $\epsilon$-expectedly feasible variant at $O(s\log s + \sqrt{s}\,\epsilon^{-1})$. The proof transfers stochastic suboptimality of the penalty problem into a deterministic feasibility bound through Lemma 1, so the noise only enters the optimality gap while the constraint violation stays deterministic.
Load-bearing premise
The deterministic constraint-violation guarantee depends on a uniform almost-sure bound on the norm of the stochastic gradient over the whole feasible domain; without that bound the method's output can only be certified in expectation or with high probability, not surely.
Editorial extensions
If this is right
- Infinite-sample stochastic convex problems with deterministic constraints admit $\epsilon$-SFSO solutions at $O(\epsilon^{-2})$ gradient evaluations, the same order as the unconstrained case, so the constraints cost nothing in the epsilon-dependence.
- For finite sums with $m=O(1)$, Algorithm 2 finds $\epsilon$-SFSO solutions in $O(s\log s + \sqrt{s}\,\epsilon^{-3/2})$ evaluations and $\epsilon$-EFSO solutions in $O(s\log s + \sqrt{s}\,\epsilon^{-1})$.
- Combined with sample average approximation, the proposed solvers yield $O(\epsilon^{-2})$ for $\epsilon$-EFSO and either $O(\epsilon^{-3})$ or $O(\epsilon^{-5/2})$ for $\epsilon$-SFSO solutions of the original infinite-sample problem.
- In the deterministic special case $s=1$, Algorithm 2 becomes a single-loop first-order penalty method with optimal $O(\epsilon^{-1})$ or nearly optimal $\tilde O(\epsilon^{-1})$ complexity.
- The framework extends directly to affine equality constraints and to convex conic constraints $c(x)\in-K$ with an exactly computable projection, covering conic programs beyond ordinary inequalities.
Reading between the lines
- One can infer that the deterministic certificate depends on the uniform almost-sure gradient bound in Assumption 2; under heavy-tailed or unbounded noise, the randomness would leak into the constraint violation, and recovering a usable certificate would require a probabilistic analogue of that assumption.
- The penalty parameter recipes $\rho=K^{3/2}$ and $\rho=s^{2/3}K^{4/3}$ instantiate a general balance between constraint violation and objective gap, and the same trade-off could govern penalty-based stochastic and augmented Lagrangian methods beyond the two algorithms analyzed here.
- A direct stress test is to replace the uniform bound with a bounded-variance or sub-Gaussian assumption and measure how the deterministic feasibility certificate degrades, which would show when 'surely feasible' claims are genuinely available.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes first-order methods for convex stochastic or finite-sum optimization with deterministic convex constraints, targeting ε-surely feasible stochastic optimal (ε-SFSO) solutions, i.e., deterministic constraint violation at most ε and expected optimality gap at most ε. For infinite sample spaces, Algorithm 1 applies an accelerated stochastic gradient scheme once to a sequence of quadratic penalty problems; under Assumptions 1–2 it is claimed to compute an ε-SFSO solution with FO complexity O(ε^{-2}) for constant penalty parameters and Õ(ε^{-2}) for dynamic ones. For finite-sum problems, Algorithm 2 uses a modified variance-reduced accelerated scheme with exact penalty gradients, obtaining O(s log s + √s ε^{-3/2}) for ε-SFSO and O(s log s + √s ε^{-1}) for ε-EFSO when m=O(1). Section 4 analyzes SAA, yielding O(ε^{-2}) for ε-EFSO and O(ε^{-5/2}) for ε-SFSO. The proofs are detailed, with explicit constants and lemmas leading to Theorems 1–4.
Significance. The deterministic feasibility guarantee is stronger than the commonly studied expected-feasibility notion, and the claimed infinite-sample complexity O(ε^{-2}) matches the unconstrained stochastic oracle bound. The finite-sum analysis with separation of stochastic and deterministic gradient contributions is a meaningful technical contribution, and the SAA byproduct gives concrete complexity comparisons. The paper is self-contained: it proves its own Lemmas 3–10 rather than importing the central recursion, and the main rates are internally consistent. The principal caveats are the strong uniform almost-sure gradient bound required for the infinite-sample deterministic feasibility claim, and the unsupported deterministic s=1 optimal-complexity remarks.
major comments (2)
- [Assumption 2; Lemma 3; Theorem 1] The ε-SFSO guarantee of Algorithm 1 for infinite sample spaces rests essentially on the uniform almost-sure bound in Assumption 2. In Lemma 3, inequality (56) bounds the noise pathwise as ∥δ_i∥ ≤ 2G, which is the only mechanism converting the recursion for F_ρ(x_K) − F*_ρ into a deterministic bound; Lemma 1(46) then yields the deterministic constraint violation in Theorem 1. If Assumption 2 is weakened to a variance bound only, the pathwise terms γ_i∥δ_i∥ are uncontrolled, and only an in-expectation or high-probability feasibility statement follows. The abstract and Remark 1 state the O(ε^{-2}) 'surely feasible' result without flagging this restriction. I recommend adding an explicit scope-limitation statement and, if possible, a companion in-expectation feasibility result under weaker noise assumptions.
- [Remarks 3(iii), 4(iii); Theorem 3(ii); Theorem 4(ii)] The special-case deterministic O(ε^{-1}) claims are not consequences of the stated theorems. For s=1, Theorem 3(ii) with ρ = √s K = K gives the bound ∥[c(˜x_K)]_+∥ ≤ 8 L_{∇ḟ}^{1/2} D_X K^{-1/2} + ... (first displayed bound after Theorem 3(ii)), so the theorem yields O(ε^{-2}) rather than O(ε^{-1}); the K^{-1/2} term originates from the K-independent term 16 L_{∇ḟ} D_X² in Lemma 8 (80), which decays only through division by ρ. Similarly, Theorem 4(ii) bound (35) has first term 60 L_{∇ḟ}^{1/2} D_X s^{-1/4}k^{-1/2}, giving O(k^{-1/2}) for s=1. If the intended argument is that δ_t=0 in the deterministic case and the noise term vanishes, that analysis must be supplied; otherwise Remarks 3(iii) and 4(iii) should be corrected.
minor comments (4)
- [Section 6.2, after eq. (110)] There is a typo: 'togther' should be 'together'.
- [Notation, Section 1.1] In Assumption 2, the variance bound E∥∇f~(x,ξ)−∇f(x)∥² ≤ σ² is implied by the uniform almost-sure bound G via σ ≤ 2G; stating both is fine, but the redundancy could be noted.
- [Section 4, Approach 2] The equality O(s log s + √s ε^{-3/2}) = O(ε^{-5/2}) suppresses the logarithmic factor in s; writing O(ε^{-5/2} log(1/ε)) would be more precise.
- [Algorithm 2, line 11] The notation ˜x_{k+1} = Σ_{t=1}^{T_k} θ_t x_t / Σ_{t=1}^{T_k} θ_t is clear, but the dependence of θ_t on k is implicit; a subscript θ_{k,t} would aid readability.
Circularity Check
No significant circularity: the epsilon-SFSO bounds are derived from the stated assumptions via in-paper penalty and ASG/SVRG lemmas; the only self-citation is a non-load-bearing external benchmark.
full rationale
The derivation chain is self-contained. The deterministic feasibility guarantee is not assumed; it is produced by Lemma 1's penalty/Lagrange multiplier inequality and, in the infinite-sample case, by Lemmas 3 and 4, where Assumption 2's uniform bound max_{ξ∈Ξ} ||∇f˜(x,ξ)|| ≤ G is used explicitly (e.g., equation (56)) to control the noise pathwise. This is a stated assumption rather than a hidden restatement of the conclusion, so Theorem 1's “surely feasible” claim is conditional on that assumption but not circular. For the finite-sum case, Algorithm 2's SVRG estimator is analyzed in Lemmas 5–7 with the deterministic component gradient computed exactly, and the penalty parameter choices in Theorem 3 are chosen after the rates are derived, not fit to the target guarantee. The only overlap with the authors' prior work is reference [23] in Section 4, which is cited alongside [17] and [37] as one of several deterministic solvers used to convert a sample-average solution into an ε-SFSO solution. That citation is a comparison benchmark, not an input to the main derivation; removing it would not change Algorithms 1–2 or Theorems 1–4. Hence there is no circular step that reduces a prediction to its inputs by construction.
Assumptions & free parameters
assumptions (4)
- domain assumption Assumption 1: X is bounded (diameter D_X), F has bounded variation D_F on X, each c_i is Lipschitz smooth with bounded magnitude, and the set of optimal Lagrange multipliers Lambda* is nonempty.
- domain assumption Assumption 2: f(x)=E[f~(x,xi)] is L_nabla_f-smooth, E[grad f~(x,xi)]=grad f(x), E[||grad f~(x,xi)-grad f(x)||^2] <= sigma^2, and max_{xi in Xi} ||grad f~(x,xi)|| <= G for all x in X.
- domain assumption Assumption 3: each f_i is L_i-smooth on X.
- domain assumption Assumption 4: there exists V > 0 such that |f~(x,xi)-f~(x',xi')| <= V for all (x,xi), (x',xi') in X x Xi.
Cite this review
Pith. "Pith review of First-order methods for stochastic and finite-sum convex optimization with deterministic constraints." pith.science (2026). https://pith.science/paper/Y5OLNMCN
@misc{pith2026250620630,
author = {Pith},
title = {Pith review of: First-order methods for stochastic and finite-sum convex optimization with deterministic constraints},
year = {2026},
howpublished = {\url{https://pith.science/paper/Y5OLNMCN}},
note = {Machine review of arXiv:2506.20630}
}
abstract
In this paper, we study a class of stochastic and finite-sum convex optimization problems with deterministic constraints. Existing methods typically aim to find an $\epsilon$-$expectedly\ feasible\ stochastic\ optimal$ solution, in which the expected constraint violation and expected optimality gap are both within a prescribed tolerance $\epsilon$. However, in many practical applications, constraints must be nearly satisfied with certainty, rendering such solutions potentially unsuitable due to the risk of substantial violations. To address this issue, we propose stochastic first-order methods for finding an $\epsilon$-$surely\ feasible\ stochastic\ optimal$ ($\epsilon$-SFSO) solution, where the constraint violation is deterministically bounded by $\epsilon$ and the expected optimality gap is at most $\epsilon$. Our methods apply an accelerated stochastic gradient (ASG) scheme or a modified variance-reduced ASG scheme $only\ once$ to a sequence of quadratic penalty subproblems with appropriately chosen penalty parameters. We establish first-order oracle complexity bounds for the proposed methods in computing an $\epsilon$-SFSO solution. As a byproduct, we also derive first-order oracle complexity results for sample average approximation method in computing an $\epsilon$-SFSO solution of the stochastic optimization problem using our proposed methods to solve the sample average problem.
Figures
Forward citations
Cited by 1 Pith paper
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Reviewed August 6, 2026 · model on record in the stance chip above.
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