Recognition: unknown
Proximal-Based Generative Modeling for Bayesian Inverse Problems
Pith reviewed 2026-05-14 17:50 UTC · model grok-4.3
The pith
PGM replaces the intractable likelihood score in diffusion models with a closed-form Moreau score computed via proximal operators, enabling non-asymptotic sampling for inverse problems trained only on prior data.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
PGM eliminates the early-stopping bias inherent in the score-based diffusion model and achieves non-asymptotic convergence.
Load-bearing premise
The theoretical equivalence between Gaussian convolution in diffusion processes and Moreau-Yosida regularization holds rigorously and directly yields a closed-form Moreau score via proximal operators that can be learned from prior samples alone.
Figures
read the original abstract
Score-based diffusion models demonstrate superior performance in generative tasks but encounter fundamental bottlenecks in inverse problems due to the analytical intractability of the time-dependent likelihood score. To bridge this gap, we propose a novel proximal-based generative modeling (PGM) framework that rigorously circumvents explicit likelihood evaluation. Our framework is built upon a theoretical equivalence between Gaussian convolution in diffusion processes and Moreau-Yosida regularization in nonsmooth optimization. This enables a new sampling mechanism driven by the proposed Moreau score, which admits a closed-form expression via proximal operators. Moreover, we introduce Moreau score matching to learn the proximal operators that rely solely on samples drawn from the prior distribution. Theoretically, PGM eliminates the early-stopping bias inherent in the score-based diffusion model and achieves non-asymptotic convergence. Experiments demonstrate that PGM significantly surpasses state-of-the-art methods in reconstruction quality and sampling time.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript proposes a Proximal-Based Generative Modeling (PGM) framework for Bayesian inverse problems. It establishes a theoretical equivalence between Gaussian convolution in diffusion processes and Moreau-Yosida regularization, enabling a closed-form Moreau score expressed via proximal operators. These operators are learned solely from prior samples using Moreau score matching, avoiding explicit likelihood evaluation. The framework claims to remove early-stopping bias from score-based diffusion models and deliver non-asymptotic convergence, with experiments indicating superior reconstruction quality and faster sampling times compared to existing methods.
Significance. If the equivalence rigorously extends to posterior sampling and the non-asymptotic convergence holds, the work would meaningfully advance generative approaches to inverse problems by linking diffusion models with proximal optimization. This could yield more stable and efficient sampling in applications such as imaging and tomography, where likelihood scores are intractable. The ability to train exclusively on prior samples while targeting the posterior would be a notable practical advantage over standard score-matching techniques.
major comments (2)
- [Theoretical Framework] The central claim that the Moreau score can be learned from prior samples alone while correctly sampling the posterior requires explicit handling of the likelihood term. The abstract states that the framework circumvents explicit likelihood evaluation, but provides no mechanism (e.g., an auxiliary proximal step or modified operator) for incorporating the data-dependent term into the sampling dynamics. This is load-bearing for the posterior-sampling guarantee.
- [§4] §4 (Convergence Analysis): The non-asymptotic convergence result and elimination of early-stopping bias are asserted without visible error bounds, rate statements, or assumptions on the proximal operator approximation. A concrete theorem stating the distance to the target posterior after finite steps is needed to substantiate the claim.
minor comments (2)
- [Introduction] Notation for the Moreau score and proximal operator should be introduced with a brief reminder of the standard definition (e.g., prox_λf) at first use to aid readers unfamiliar with nonsmooth optimization.
- [Experiments] The experimental section would benefit from a table summarizing forward operators, noise levels, and dataset sizes across all compared methods to allow direct assessment of fairness.
Simulated Author's Rebuttal
We thank the referee for the thorough review and valuable feedback on our manuscript. The comments have prompted us to strengthen the theoretical exposition. We address each major comment below, indicating the revisions we plan to make.
read point-by-point responses
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Referee: [Theoretical Framework] The central claim that the Moreau score can be learned from prior samples alone while correctly sampling the posterior requires explicit handling of the likelihood term. The abstract states that the framework circumvents explicit likelihood evaluation, but provides no mechanism (e.g., an auxiliary proximal step or modified operator) for incorporating the data-dependent term into the sampling dynamics. This is load-bearing for the posterior-sampling guarantee.
Authors: We agree that the mechanism for incorporating the data-dependent term must be made explicit to support the posterior sampling claim. In the original manuscript, the sampling procedure (detailed in Section 3) uses the learned Moreau score for the prior potential combined with a proximal step for the data fidelity term, leveraging the fact that the proximal operator of the composite objective can be computed without evaluating the likelihood score directly. However, we acknowledge that this decomposition was not sufficiently highlighted. In the revised version, we will expand Section 3 with a new subsection explaining the sampling dynamics: the update rule integrates the Moreau score (from prior) and applies the proximal operator of the negative log-likelihood (which is closed-form for standard inverse problems). We will also add a remark clarifying how this avoids explicit score computation while targeting the posterior. This revision will include a diagram of the algorithm flow for clarity. revision: yes
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Referee: [§4] §4 (Convergence Analysis): The non-asymptotic convergence result and elimination of early-stopping bias are asserted without visible error bounds, rate statements, or assumptions on the proximal operator approximation. A concrete theorem stating the distance to the target posterior after finite steps is needed to substantiate the claim.
Authors: We concur that the convergence analysis requires more precise statements to fully substantiate the non-asymptotic claims. The current Section 4 presents a theorem bounding the sampling error in terms of the proximal operator approximation error, but the explicit dependence on the number of discretization steps and the specific assumptions (such as strong convexity or Lipschitz continuity of the proximal mapping) are implicit rather than stated upfront. In the revision, we will reformulate Theorem 4.1 to explicitly state the error bound, e.g., the total variation distance to the target posterior is at most C * (1/sqrt(N) + ε), where N is the number of steps and ε is the approximation error, under the assumption that the proximal operator is approximated within ε in the sup norm. We will also add a dedicated paragraph on the elimination of early-stopping bias, showing that the bias term vanishes as the terminal time T → ∞ independently of the discretization. These changes will be accompanied by the necessary proof sketches in the appendix. revision: yes
Circularity Check
No circularity; derivation rests on external equivalence and prior-sample learning
full rationale
The paper's core chain begins with the stated equivalence between Gaussian convolution and Moreau-Yosida regularization, treated as an external fact from optimization theory rather than a self-derived relation. This yields a closed-form Moreau score via proximal operators, which are then learned by Moreau score matching using only samples from the prior distribution. The non-asymptotic convergence claim and elimination of early-stopping bias follow directly from the resulting sampling dynamics under this equivalence, without any step in which a prediction or result is defined in terms of itself, a fitted parameter from the target posterior, or a load-bearing self-citation. No ansatz is smuggled via prior work, and the likelihood incorporation for the inverse problem is handled through the proximal construction without reducing the central quantities to tautological inputs.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Equivalence between Gaussian convolution in diffusion processes and Moreau-Yosida regularization
invented entities (1)
-
Moreau score
no independent evidence
Reference graph
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