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arxiv: 2407.11703 · v1 · pith:BPBF4IP4new · submitted 2024-07-16 · 🧮 math.OC · cs.NA· math.NA

Numerical Eigenvalue Optimization by Shape-Variations for Maxwell's Eigenvalue Problem

Pith reviewed 2026-05-23 22:54 UTC · model grok-4.3

classification 🧮 math.OC cs.NAmath.NA
keywords Maxwell eigenvalue problemshape optimizationadjoint methoddomain variationsmixed finite elementsBFGS optimizationelectromagnetic resonance
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The pith

Normalization of eigenfunctions yields adjoint formulas for eigenvalue derivatives under domain variations, enabling shape optimization of Maxwell eigenvalues via damped inverse BFGS.

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

The paper derives adjoint-based sensitivities for Maxwell eigenvalues with respect to domain shape changes. It starts from the mixed variational formulation on a reference domain using Piola-type mappings, then normalizes eigenfunctions to secure local uniqueness. This normalization permits explicit adjoint expressions for the derivatives that feed into a damped inverse BFGS optimizer. The method is discretized with mixed finite elements and tested on a numerical example that drives an eigenvalue to a prescribed target. A reader would care because resonant frequencies in electromagnetic devices are directly controlled by geometry, and the approach supplies a concrete computational route for that control.

Core claim

After the mixed formulation of the Maxwell eigenvalue problem is pulled back to a fixed reference domain via suitable transformations, normalization of the eigenfunctions produces local uniqueness and thereby allows derivation of adjoint formulas for the eigenvalue derivatives with respect to domain variations; these formulas are inserted into a damped inverse BFGS algorithm whose positive-definiteness and line-search properties are retained, and the resulting optimization problem is discretized by mixed finite elements.

What carries the argument

Adjoint formulas for the derivatives of the eigenvalues with respect to domain variations, obtained after normalization of the eigenfunctions in the mixed formulation.

If this is right

  • Target eigenvalue values are reached by repeated small deformations of the computational domain.
  • The optimization stays on a fixed reference mesh because all quantities are pulled back via the domain mapping.
  • The damped inverse BFGS iteration preserves positive definiteness while simplifying the line search.
  • Mixed finite-element discretization of the pulled-back problem produces the discrete sensitivities used in each step.

Where Pith is reading between the lines

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

  • The same normalization-plus-adjoint pattern could be applied to other Maxwell-type problems once an analogous mixed formulation exists.
  • Convergence of the optimizer may slow when the normalization constant approaches zero near eigenvalue crossings.
  • Extending the single-eigenvalue objective to a weighted sum of several eigenvalues would require only additional adjoint solves.

Load-bearing premise

Normalization of the eigenfunctions produces local uniqueness of the solution and thereby permits the adjoint formulas to be derived.

What would settle it

A concrete domain deformation for which the eigenvalue derivative computed from the adjoint formula differs from the value obtained by finite-difference perturbation of the same normalized eigenpair.

Figures

Figures reproduced from arXiv: 2407.11703 by Christine Herter, Sebastian Sch\"ops, Winnifried Wollner.

Figure 1
Figure 1. Figure 1: Electric field of the TM010, also called π-mode The analytic sensitives of eigenpairs of Maxwell’s eigenvalue problem have been considered in isogeometric analysis, e.g., in work of [54], where the sensitivities of the eigenpair have been computed with respect to a scalar parameter. The therein parameter optimization has been done with a simplified formulation of Maxwell’s eigenvalue problem excluding the … view at source ↗
Figure 2
Figure 2. Figure 2: Geometry of a Cavity [PITH_FULL_IMAGE:figures/full_fig_p012_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Mesh of the 5-cell Cavity BFGS method converges after 16 iterations. For a setting with 5438 DoFs, it takes 12. The values of Jq are slightly smaller than 1, which means that we obtain a small shrinkage of the domain. The deformation of a 5-cell cavity after optimization is shown in [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Deformation of a 5-cell cavity after optimization of the first eigenvalue to target value λ∗ = 6017 using the BFGS method from algorithm 1 with regularization parameters α = 100 and β = 10−6 . The chosen refinement level is 2, the number of DoFs is 86723. Lagrange elements of order 1 and lowest order Nédélec elements are used. order to solve this optimization problem, we discussed a damped inverse BFGS met… view at source ↗
read the original abstract

In this paper we consider the free-form optimization of eigenvalues in electromagnetic systems by means of shape-variations with respect to small deformations. The objective is to optimize a particular eigenvalue to a target value. We introduce the mixed variational formulation of the Maxwell eigenvalue problem introduced by Kikuchi (1987) in function spaces of (H(\operatorname{curl}; \Omega)) and (H^1(\Omega)). To handle this formulation, suitable transformations of these spaces are utilized, e.g., of Piola-type for the space of (H(\operatorname{curl}; \Omega)). This allows for a formulation of the problem on a fixed reference domain together with a domain mapping. Local uniqueness of the solution is obtained by a normalization of the the eigenfunctions. This allows us to derive adjoint formulas for the derivatives of the eigenvalues with respect to domain variations. For the solution of the resulting optimization problem, we develop a particular damped inverse BFGS method that allows for an easy line search procedure while retaining positive definiteness of the inverse Hessian approximation. The infinite dimensional problem is discretized by mixed finite elements and a numerical example shows the efficiency of the proposed approach.

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

1 major / 2 minor

Summary. The paper develops a shape-optimization method for Maxwell eigenvalues via domain variations. It employs Kikuchi's mixed variational formulation in (H(curl), H^1) spaces, applies Piola-type transformations to map to a fixed reference domain, invokes normalization of eigenfunctions to obtain local uniqueness, derives adjoint formulas for eigenvalue derivatives with respect to the domain, solves the resulting problem with a damped inverse BFGS algorithm, discretizes via mixed finite elements, and demonstrates the approach on a numerical example.

Significance. If the adjoint derivation holds, the work supplies a concrete, implementable pipeline that combines established domain-mapping and adjoint techniques with a specialized quasi-Newton solver for electromagnetic eigenvalue shape optimization. The numerical example provides evidence of practical efficiency in the mixed-FEM setting.

major comments (1)
  1. [Abstract, §3] Abstract and §3: The claim that normalization of the eigenfunctions produces local uniqueness permitting derivation of the adjoint formulas for dλ/dΩ does not address multiplicity. When the target eigenvalue has multiplicity ≥2, the normalization (typically an L2-type constraint) leaves a circle of equivalent eigenfunctions; the shape derivative becomes set-valued and the adjoint construction in the mixed (H(curl),H^1) setting does not automatically select a unique representative. No assumption that the eigenvalue remains simple under the domain variations, nor any selection mechanism (phase fixing, orthogonalization), is stated.
minor comments (2)
  1. [Abstract] Abstract contains the repeated article 'the the eigenfunctions'.
  2. [§4] The description of the damped inverse BFGS line-search procedure and the precise form of the inverse-Hessian update should be expanded for reproducibility.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive comment. We address the major point on eigenvalue multiplicity below.

read point-by-point responses
  1. Referee: [Abstract, §3] Abstract and §3: The claim that normalization of the eigenfunctions produces local uniqueness permitting derivation of the adjoint formulas for dλ/dΩ does not address multiplicity. When the target eigenvalue has multiplicity ≥2, the normalization (typically an L2-type constraint) leaves a circle of equivalent eigenfunctions; the shape derivative becomes set-valued and the adjoint construction in the mixed (H(curl),H^1) setting does not automatically select a unique representative. No assumption that the eigenvalue remains simple under the domain variations, nor any selection mechanism (phase fixing, orthogonalization), is stated.

    Authors: We agree that the manuscript does not explicitly discuss the case of multiple eigenvalues. The derivation of the adjoint sensitivity formulas in Section 3 relies on the assumption that the eigenvalue λ is simple. Under this assumption, the normalization condition provides the necessary local uniqueness to differentiate the eigenvalue with respect to the domain. For eigenvalues with multiplicity greater than one, the shape derivative is indeed set-valued, and the adjoint approach as presented would require additional selection criteria, such as phase fixing or orthogonalization to a reference eigenfunction. In our numerical example, the optimized eigenvalue remains simple throughout the iterations. We will revise the abstract and Section 3 to explicitly state the simplicity assumption and briefly note the limitation for multiple eigenvalues. revision: yes

Circularity Check

0 steps flagged

No circularity; derivation from external Kikuchi formulation and standard domain-mapping arguments

full rationale

The paper's central steps derive adjoint formulas for eigenvalue shape derivatives from the mixed variational formulation (Kikuchi 1987, external citation) after normalization to obtain local uniqueness, followed by domain mapping to a reference domain and discretization. No step reduces by the paper's own equations to a fitted input renamed as prediction, self-definition of a quantity in terms of its output, or a load-bearing self-citation chain. The normalization step is presented as enabling the adjoint derivation without the result being tautological or forced by prior author work. This is the common case of an independent derivation resting on cited external foundations.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The approach rests on the pre-existing Kikuchi mixed formulation and standard assumptions of shape calculus; no new free parameters, axioms, or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption The mixed variational formulation of the Maxwell eigenvalue problem in H(curl; Ω) and H¹(Ω) introduced by Kikuchi (1987).
    Cited directly as the starting point for the formulation and subsequent transformations.

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