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arxiv: 2604.06905 · v1 · submitted 2026-04-08 · 🧮 math.AP

Inverse problems for the spectral fractional Laplacian with inhomogeneous Dirichlet boundary data

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classification 🧮 math.AP
keywords spectral fractional LaplacianDirichlet-to-Neumann mapinverse problemdensity resultinhomogeneous Dirichlet datanonlocal operatorsboundary measurements
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The pith

A Dirichlet-to-Neumann map recovers information about the spectral fractional Laplacian from inhomogeneous boundary data.

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

The paper studies the spectral fractional Laplacian when the Dirichlet boundary data is allowed to be inhomogeneous. It defines a Dirichlet-to-Neumann map that sends the boundary input to the corresponding Neumann output and uses this map to analyze an inverse problem of recovering the operator. A separate density result is established for the operator itself. Readers would care because the map turns internal nonlocal properties into observable boundary quantities, which is a standard route to uniqueness and reconstruction in inverse problems for PDEs. The density result supplies a technical tool that often closes approximation arguments in such settings.

Core claim

The authors introduce a Dirichlet-to-Neumann map for the spectral fractional Laplacian with inhomogeneous Dirichlet boundary data and analyze an associated inverse problem; they also establish an additional density result for the spectral fractional Laplacian.

What carries the argument

The Dirichlet-to-Neumann map for the spectral fractional Laplacian with inhomogeneous Dirichlet boundary data, which encodes boundary measurements and supports the inverse analysis.

Load-bearing premise

The spectral fractional Laplacian with inhomogeneous Dirichlet boundary data admits a well-defined Dirichlet-to-Neumann map in appropriate function spaces.

What would settle it

An explicit counterexample on a bounded domain where the map cannot be defined continuously or where two different spectral fractional Laplacians produce the same boundary map would disprove the central claims.

read the original abstract

In this paper, we study the spectral fractional Laplacian with inhomogeneous Dirichlet boundary data. Our contributions are twofold: first we introduce a Dirichlet-to-Neumann map for this operator and analyze an associated inverse problem; and second we establish an additional density result for the spectral fractional Laplacian.

Editorial analysis

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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

0 major / 2 minor

Summary. The paper studies the spectral fractional Laplacian on bounded C^∞ domains, defined via eigenfunction expansion of the Dirichlet Laplacian. It introduces a Dirichlet-to-Neumann map by handling inhomogeneous boundary data through a continuous lifting operator into fractional Sobolev spaces, proves the map is well-defined and bounded, and analyzes the inverse problem of recovering a potential from the DtN map with uniqueness via an integral identity. It also establishes a density result using mollification and cutoff arguments adapted to the spectral definition.

Significance. If the constructions and proofs hold, this extends the theory of nonlocal operators to inhomogeneous Dirichlet data, which is practically relevant. The well-defined DtN map and uniqueness result for the inverse problem provide new tools for coefficient recovery, while the density result supports functional-analytic approximations. The approach via eigenexpansions and liftings is a standard but carefully executed contribution to inverse problems for fractional Laplacians.

minor comments (2)
  1. [§2] §2: The lifting operator for inhomogeneous data is introduced via continuous extension into the fractional Sobolev space; adding an explicit remark on the dependence of its operator norm on the C^∞ domain regularity would improve clarity.
  2. [§4] §4: In the uniqueness argument for the inverse problem, the integral identity is used with suitable test functions; a brief justification of why these functions lie in the precise duality space (to ensure the pairing is well-defined) would remove any potential ambiguity.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive and accurate summary of our manuscript, which correctly identifies the introduction of the Dirichlet-to-Neumann map for the spectral fractional Laplacian with inhomogeneous data, the uniqueness result for the inverse problem via the integral identity, and the density result obtained through mollification and cutoff arguments. We appreciate the recommendation for minor revision.

Circularity Check

0 steps flagged

No significant circularity; derivation self-contained via spectral definitions and standard analysis

full rationale

The manuscript defines the spectral fractional Laplacian via eigenfunction expansion of the Dirichlet Laplacian on a bounded smooth domain, introduces a continuous lifting operator to handle inhomogeneous Dirichlet data in fractional Sobolev spaces, and establishes the Dirichlet-to-Neumann map as a bounded operator between trace space and dual. The inverse problem recovers coefficients from this map via an integral identity obtained directly from the weak formulation. The density result follows from mollification and cutoff functions respecting the spectral definition. No equation reduces to a prior fitted parameter, self-citation chain, or definitional tautology; all steps are independent constructions or proofs using functional analysis. This matches the default expectation for a pure-mathematics paper with no load-bearing self-referential reductions.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only abstract available; no explicit free parameters, axioms, or invented entities can be identified. The work presumably relies on standard functional analysis assumptions for fractional Sobolev spaces and spectral definitions of the Laplacian.

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