A modified Riemannian Levenberg-Marquardt Algorithm for robust or constraint optimization on manifolds
Pith reviewed 2026-06-26 07:10 UTC · model grok-4.3
The pith
A robust version of the Riemannian Levenberg-Marquardt algorithm handles optimization problems with outliers on manifolds.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We extend the Levenberg-Marquardt method on Riemannian manifolds to a robust variant that allows to tackle problems from applications where outliers are to be expected. We formally state the framework for a block-wise variant of the Robust Riemannian Levenberg-Marquardt algorithm and discuss how known convergence results can be applied here as well. We further discuss several alternatives for phrasing the sub problem that has to be solved. Finally we illustrate how the accompanying open source implementation can be used to efficiently solve problems such as geodesic regression, Procrustes analysis, subspace Procrustes analysis and bundle adjustment robustly and compare the Levenberg-Marquard
What carries the argument
The block-wise variant of the Robust Riemannian Levenberg-Marquardt algorithm, which modifies the iteration to incorporate a robust loss function for outlier resistance while operating on the manifold.
If this is right
- The algorithm solves geodesic regression robustly even when some data points are outliers.
- It applies directly to robust Procrustes analysis and subspace Procrustes analysis on manifolds.
- Bundle adjustment tasks can be solved robustly using this Levenberg-Marquardt approach.
- Existing convergence results carry over to the robust block-wise case without additional proof.
- Several phrasing options for the inner subproblem give implementers flexibility in code.
Where Pith is reading between the lines
- The block-wise structure may support efficient handling of large or distributed data sets on manifolds.
- Similar robust modifications could be tested on other Riemannian solvers such as trust-region methods.
- The approach may extend to constraint optimization on manifolds by treating constraints through the robust loss.
- Open implementations could enable direct comparisons across multiple robust manifold problems in applied fields.
Load-bearing premise
The block-wise robust formulation inherits convergence guarantees from earlier non-robust Riemannian LM analyses without requiring new proofs or additional regularity conditions on the robust loss function.
What would settle it
A concrete manifold problem with known outliers where the block-wise robust LM fails to converge, while the corresponding non-robust version succeeds, would show that the convergence inheritance does not hold.
Figures
read the original abstract
We extend the Levenberg-Marquardt method on Riemannian manifolds to a robust variant that allows to tackle problems from applications where outliers are to be expected. We formally state the framework for a block-wise variant of the Robust Riemannian Levenberg-Marquardt algorithm and discuss how known convergence results can be applied here as well. We further discuss several alternatives for phrasing the sub problem that has to be solved. Finally we illustrate how the accompanying open source implementation in Manopt$.$jl can be used to efficiently solve problems such as geodesic regression, Procrustes analysis, subspace Procrustes analysis and bundle adjustment robustly and compare the Levenberg-Marquardt solver to other solvers for nonsmooth Riemannian optimization.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper extends the Riemannian Levenberg-Marquardt method to a robust variant for optimization problems with outliers. It formally states a block-wise formulation of the Robust Riemannian Levenberg-Marquardt algorithm, discusses applicability of existing convergence results to this variant, presents alternatives for phrasing the subproblem, and demonstrates an open-source implementation in Manopt.jl on examples including geodesic regression, Procrustes analysis, subspace Procrustes analysis, and bundle adjustment, with comparisons to other nonsmooth Riemannian solvers.
Significance. If the convergence inheritance holds, the work supplies a practical, reproducible algorithmic tool for robust manifold optimization in applications prone to outliers (e.g., computer vision tasks). The open-source Manopt.jl implementation and explicit discussion of subproblem alternatives constitute concrete strengths that enhance usability.
major comments (2)
- [§4] §4 (convergence discussion): The statement that 'known convergence results can be applied here as well' is not accompanied by any verification that the robust loss function preserves the smoothness, Lipschitz-gradient, or Hessian-regularity assumptions required by the cited non-robust Riemannian LM theorems. This directly undermines the central claim that the block-wise robust framework inherits those guarantees without additional analysis.
- [§2] §2 (framework statement): The robust loss is never explicitly defined or stated (e.g., no formula for the Huber or other loss, no discussion of its differentiability properties). Without this, it is impossible to confirm that the local quadratic model structure of the LM step remains valid or that nondifferentiability points do not appear, rendering the block-wise extension's theoretical grounding incomplete.
minor comments (2)
- The title refers to 'constraint optimization' but the abstract and body focus exclusively on the robust case; a clarifying sentence on whether constraints are also treated would improve scope alignment.
- In the numerical examples section, the comparison metrics (e.g., iteration counts, final cost, robustness to outlier percentage) should be tabulated for reproducibility.
Simulated Author's Rebuttal
We thank the referee for their careful reading and constructive feedback on the manuscript. We address the two major comments point by point below, committing to revisions that strengthen the theoretical presentation without altering the core contributions.
read point-by-point responses
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Referee: [§2] §2 (framework statement): The robust loss is never explicitly defined or stated (e.g., no formula for the Huber or other loss, no discussion of its differentiability properties). Without this, it is impossible to confirm that the local quadratic model structure of the LM step remains valid or that nondifferentiability points do not appear, rendering the block-wise extension's theoretical grounding incomplete.
Authors: We agree that an explicit definition of the robust loss is required for rigor. The revised manuscript will include the precise formula for the robust loss function (e.g., the Huber loss or a smoothed variant) together with a discussion of its differentiability properties. We will clarify that the local quadratic model in the LM step is constructed from the gradient of the loss and a regularized approximation to the Hessian, with explicit handling of points of nondifferentiability via one-sided derivatives or local smoothing to ensure the subproblem remains well-defined. This addition directly addresses the completeness of the block-wise framework's theoretical grounding. revision: yes
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Referee: [§4] §4 (convergence discussion): The statement that 'known convergence results can be applied here as well' is not accompanied by any verification that the robust loss function preserves the smoothness, Lipschitz-gradient, or Hessian-regularity assumptions required by the cited non-robust Riemannian LM theorems. This directly undermines the central claim that the block-wise robust framework inherits those guarantees without additional analysis.
Authors: The manuscript's statement in §4 is intentionally concise because the block-wise formulation is designed to inherit the structure of the original LM subproblem. However, we accept that explicit verification of the assumptions for the robust loss is necessary to support the inheritance claim. In the revision we will expand §4 to state the precise conditions (C^1 smoothness, Lipschitz continuity of the gradient, and bounded Hessian regularity) under which the cited theorems apply, verify them for standard robust losses such as Huber (or note when smoothing is required), and qualify the claim accordingly. If a chosen loss violates an assumption, we will either restrict the statement or reference available nonsmooth extensions. revision: yes
Circularity Check
No circularity: algorithmic extension with external convergence inheritance
full rationale
The paper describes an algorithmic construction extending Riemannian LM to a block-wise robust variant and states that known convergence results from prior non-robust analyses can be applied. No equations, fitted parameters, or self-definitional reductions appear in the provided abstract or description. The central claim is an extension plus discussion of applicability of external results; no load-bearing step reduces by construction to the paper's own inputs, self-citations, or renamed empirical patterns. This is a standard case of an honest non-finding for an algorithmic paper.
Axiom & Free-Parameter Ledger
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