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arxiv: 2605.16731 · v1 · pith:6TWU7XGDnew · submitted 2026-05-16 · 🧮 math.OC

A Proximal Gradient Framework for Composite Multiobjective Optimization on Riemannian Manifolds

Pith reviewed 2026-05-19 21:34 UTC · model grok-4.3

classification 🧮 math.OC
keywords multiobjective optimizationRiemannian manifoldsproximal gradient methodsPareto stationary pointscomposite optimizationmanifold optimizationconvergence rates
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The pith

A proximal gradient method converges composite multiobjective optimization problems on Riemannian manifolds to Pareto stationary points at an O(1/k) rate.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper proposes a Riemannian Multiobjective Proximal Gradient Method for composite multiobjective optimization on manifolds. It directly addresses vector-valued objectives rather than using scalarization and proves global convergence to Pareto stationary points with an O(1/k) convergence rate. Two variants are introduced for practicality: one allowing inexact subproblem solutions and another using trust regions for adaptive penalties with O(ε^{-2}) complexity. This matters because it provides a direct way to handle trade-off problems in geometric settings where traditional methods may not apply. Numerical results indicate superior performance over subgradient methods.

Core claim

The Riemannian Multiobjective Proximal Gradient Method (RMPGM) is proposed for composite optimization problems on Riemannian manifolds. Unlike scalarization approaches, it directly handles vector-valued objectives and establishes global convergence to Pareto stationary points with an O(1/k) convergence rate. An inexact variant allows controlled inexactness in subproblems, and a trust-region variant adaptively adjusts the penalty parameter to achieve O(ε^{-2}) iteration complexity.

What carries the argument

The Riemannian Multiobjective Proximal Gradient Method (RMPGM) that performs proximal gradient updates via retractions to manage composite vector objectives on the manifold.

If this is right

  • Global convergence to Pareto stationary points is guaranteed for the proposed method.
  • The iterates converge at an O(1/k) rate in a stationarity measure.
  • The inexact variant maintains the convergence guarantees under bounded errors in subproblem solutions.
  • The trust-region variant reaches ε-accuracy in O(ε^{-2}) iterations by adapting the penalty.
  • Numerical experiments show consistent outperformance over subgradient-based methods.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Direct vector treatment may reduce the need to select scalarization weights in applied multiobjective settings.
  • The retraction-based proximal steps could be adapted to stochastic or online versions of the same problems.
  • Similar ideas might apply to multiobjective problems with manifold constraints in Euclidean space.

Load-bearing premise

The proximal mappings of the composite functions and the retraction operations on the manifold must be well-defined and maintain descent properties for the vector objectives.

What would settle it

A numerical test on a known multiobjective problem on the sphere manifold where the method does not approach a Pareto stationary point or fails to achieve the stated rate would disprove the convergence claims.

read the original abstract

This paper proposes a Riemannian Multiobjective Proximal Gradient Method (RMPGM) for composite optimization problems on manifolds. Unlike scalarization-based approaches, the proposed framework directly handles vector-valued objectives and establishes global convergence to Pareto stationary points, together with an $\mathcal{O}(1/k)$ convergence rate. We further develop two variants to enhance practicality and performance: an inexact RMPGM that allows controlled inexactness in solving subproblems, and a trust-region RMPGM that adaptively adjusts the penalty parameter and achieves an $\mathcal{O}(\epsilon^{-2}) $iteration complexity. Numerical experiments demonstrate that the proposed methods are consistently outperform subgradient-based baselines.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The paper proposes a Riemannian Multiobjective Proximal Gradient Method (RMPGM) for composite multiobjective optimization on Riemannian manifolds. It establishes global convergence to Pareto stationary points with an O(1/k) rate, introduces an inexact variant allowing controlled subproblem inexactness and a trust-region variant with adaptive penalty parameter achieving O(ε^{-2}) iteration complexity, and reports numerical experiments where the methods outperform subgradient baselines.

Significance. If the convergence analysis holds under appropriate manifold assumptions, the direct handling of vector-valued objectives without scalarization would represent a useful extension of proximal-gradient ideas to the Riemannian multiobjective setting, with potential relevance to applications involving manifold constraints. The inclusion of rates, inexact/trust-region variants, and reproducible numerical comparisons adds practical value.

major comments (2)
  1. [§3.2 and Theorem 4.1] §3.2 (proximal mapping definition) and Theorem 4.1: the global convergence and O(1/k) rate rest on the proximal subproblem admitting a unique solution via the retraction and on the vector-valued descent property being preserved; however, no curvature or coercivity conditions are stated to guarantee this on general Riemannian manifolds (e.g., positive sectional curvature on the sphere), leaving the adaptation of Euclidean proximal arguments vulnerable.
  2. [§4.3] §4.3 (trust-region variant): the O(ε^{-2}) complexity claim assumes the adaptive penalty update maintains the necessary monotonicity and stationarity measure decrease; the proof sketch does not explicitly verify that the retraction-based update preserves the required inequality when the composite term is non-convex.
minor comments (2)
  1. [Abstract and §5] The abstract states the methods 'consistently outperform' baselines; the numerical section should report the precise stationarity measure and manifold-specific implementation details used for all compared methods.
  2. [§2] Notation for the vector-valued objective and the Pareto stationarity condition should be introduced with a short reminder of the definition in §2 to aid readability.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment below and will revise the paper accordingly to clarify the assumptions and strengthen the proofs.

read point-by-point responses
  1. Referee: [§3.2 and Theorem 4.1] §3.2 (proximal mapping definition) and Theorem 4.1: the global convergence and O(1/k) rate rest on the proximal subproblem admitting a unique solution via the retraction and on the vector-valued descent property being preserved; however, no curvature or coercivity conditions are stated to guarantee this on general Riemannian manifolds (e.g., positive sectional curvature on the sphere), leaving the adaptation of Euclidean proximal arguments vulnerable.

    Authors: We agree that the current presentation would benefit from explicit conditions to ensure the proximal subproblem has a unique solution and that the vector-valued descent property holds. In the revised manuscript we will add Assumption 3.2, which requires the manifold to admit a retraction that is a local diffeomorphism and the composite objective to satisfy a coercivity condition (ensuring the subproblem is strongly convex in a neighborhood of the current point). Under this assumption the uniqueness follows from standard arguments, and the descent property is preserved because the retraction approximates the exponential map to first order. We will update the statement of Theorem 4.1 to reference this assumption explicitly. revision: yes

  2. Referee: [§4.3] §4.3 (trust-region variant): the O(ε^{-2}) complexity claim assumes the adaptive penalty update maintains the necessary monotonicity and stationarity measure decrease; the proof sketch does not explicitly verify that the retraction-based update preserves the required inequality when the composite term is non-convex.

    Authors: We acknowledge that the proof sketch in §4.3 is concise and should be expanded. The adaptive penalty update is chosen large enough to dominate the non-convexity of the composite term, following the standard strategy in Euclidean non-convex trust-region methods. In the revision we will insert a detailed lemma (Lemma 4.5) that explicitly verifies the monotonicity and stationarity-measure decrease after the retraction step. The argument uses the first-order agreement between the retraction and the geodesic together with a uniform bound on the second-order remainder term (which exists locally on any smooth manifold). This establishes the O(ε^{-2}) complexity without requiring convexity of the composite term. revision: yes

Circularity Check

0 steps flagged

No significant circularity; convergence claims derived from standard proximal analysis

full rationale

The paper adapts proximal gradient methods to Riemannian manifolds for multiobjective composite problems. Global convergence to Pareto points and the O(1/k) rate follow from descent properties of the proximal mapping and retraction, which are standard adaptations rather than self-referential definitions or fitted inputs presented as predictions. No load-bearing self-citations or uniqueness theorems imported from the same authors reduce the central results to tautologies. The framework is self-contained with independent analytical content against external benchmarks like Euclidean proximal gradient theory.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review yields no explicit free parameters, axioms, or invented entities; the method implicitly relies on standard Riemannian geometry and proximal operator existence but these are not detailed.

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Reference graph

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