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arxiv: 2606.23560 · v1 · pith:2EQHTDDAnew · submitted 2026-06-22 · 🧮 math.OC

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

classification 🧮 math.OC
keywords Riemannian optimizationLevenberg-Marquardt algorithmrobust optimizationoutlier handlingmanifold optimizationgeodesic regressionbundle adjustmentProcrustes analysis
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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.

The paper extends the Levenberg-Marquardt method from Euclidean space to Riemannian manifolds in a robust way that tolerates outliers in the data. It formalizes a block-wise version of this robust algorithm and notes that existing convergence results still hold. The work also covers different ways to set up the subproblems that need solving at each step. Examples show how this can be applied to robust versions of geodesic regression, Procrustes analysis, and bundle adjustment using code in an open-source library. Readers working with data on curved spaces that contains errors would find the practical framework useful.

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

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

  • 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

Figures reproduced from arXiv: 2606.23560 by Mateusz Baran, Ronny Bergmann.

Figure 1
Figure 1. Figure 1: The original geodesic γp,X (cyan) and data qi , i = 1, . . . , 100 with outliers (purple). This yields a reconstruction with least squares regression geodesic γp∗,X∗ (sand, right) that is influ￾enced by the outliers, while the robust regression geodesic γp⋆,X⋆ (green) reconstructs the original geodesics. For visualization pur￾poses are the tangent vectors scaled by 1 2 [PITH_FULL_IMAGE:figures/full_fig_p… view at source ↗
Figure 2
Figure 2. Figure 2: Runtime comparison of our RLM (green) to the LT￾MADS algorithm (sand) on different special orthogonal groups. B as a copy of A, where we create four outliers by adding 1 10 to four entries. We then generate a random rotation matrix p ∗ by using rand(M; vector_at = Id, σ=0.5/d) to generate a random tangent vector in the tangent space of the identity matrix Id using the random functions from Manifolds.jl. We… view at source ↗
Figure 3
Figure 3. Figure 3: Cost value of the resulting special orthogonal matrix of our RLM (green) to the LTMADS algorithm (sand). d = 9 and runs for about 32.3 seconds for the largest experiment d = 15. RLM is always faster, for the larger experiments, d > 7, at least by a factor 100. While RLM solves the objective (25), i. e., a smoothened version of the original objective (24), LTMADS tackles the original, nonsmooth objective f(… view at source ↗
Figure 4
Figure 4. Figure 4: Runtime comparison of our RLM (green) to the LT￾MADS algorithm (sand) on different Stiefel manifolds. −ybT i to the tangent space JFi (p)[X] = DFi(p)[X] = −Xbi and J ∗ Fi (p)[y] = −ybT i +p·sym(−p TybT i ), where sym(A) = 1 2 (A + AT) is the projection onto the set of symmetric matrices. We run the experiment with the same settings and the same data generation as described in the last section. We just have… view at source ↗
Figure 5
Figure 5. Figure 5: Cost value of the computed minimizers on St(d, k) of our RLM (green) to the LTMADS algorithm (sand). few cases— about 0.01 % better. We additionally look at the number of iterations, each of the solver runs required, cf [PITH_FULL_IMAGE:figures/full_fig_p019_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Objective value history on the bundle-adjustment ex￾periment for SciPy TRF (Python) and our RLM (Julia). An accompanying new release of Manopt.jl provides a generic implementation of the introduced algorithm. Using this open source code, we illustrate how a robust Levenberg-Marquardt qualitatively improves geodesic regression under outliers. We further illustrate how the robust Procrustes problem can be so… view at source ↗
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.

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 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)
  1. [§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] §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)
  1. 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.
  2. 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

2 responses · 0 unresolved

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
  1. 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

  2. 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

0 steps flagged

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

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are identifiable from the abstract alone.

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Reference graph

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