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arxiv: 2604.12584 · v1 · submitted 2026-04-14 · 💻 cs.DS · cs.DM

Robust Graph Isomorphism, Quadratic Assignment and VC Dimension

Pith reviewed 2026-05-10 14:24 UTC · model grok-4.3

classification 💻 cs.DS cs.DM
keywords graph edit distanceVC dimensionquadratic assignmentWeisfeiler-Lemanapproximation algorithmsgraph isomorphismrobust testing
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The pith

VC-bounded graphs allow additive εn² approximation to graph edit distance in time n to the O(d/ε²).

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

The paper establishes approximation algorithms for graph edit distance and quadratic assignment that run in time whose exponent depends on the VC-dimension d of the input rather than on log n. This produces an additive εn² guarantee for GED on n-vertex graphs of VC-dimension d in time n^{O(d/ε²)}, recovering earlier results as the special case d = O(log n). The same machinery yields a low-dimensional Weisfeiler-Leman test for the robust isomorphism problem in which non-isomorphic pairs are promised to be at least εn² apart in edit distance.

Core claim

We present an additive εn²-approximation algorithm for the Graph Edit Distance problem on graphs of VC dimension d running in time n^{O(d/ε²)}. Similar techniques give an εn²-approximation for quadratic assignment problems with a suitable VC-dimension notion in time n^{O(ε^{-2}(d + log ε^{-1}))}. For the ε-GI problem of distinguishing isomorphic graphs from those at edit distance at least εn², the Weisfeiler-Leman algorithm with dimension O(ε^{-1}d log(ε^{-1})) suffices on VC-dimension d graphs, while dimension O(ε^{-1} log n) works for arbitrary graphs.

What carries the argument

The VC-dimension of graphs or QAP instances, which bounds the diversity of neighborhoods inducible by vertex subsets and thereby controls the search space for near-optimal alignments.

Load-bearing premise

The input graphs or QAP instances have bounded VC-dimension d.

What would settle it

A pair of VC-dimension-d graphs at edit distance at least εn² that the Weisfeiler-Leman algorithm of dimension O(ε^{-1} d log(ε^{-1})) fails to distinguish would disprove the robust isomorphism claim.

read the original abstract

We present an additive $\varepsilon n^{2}$-approximation algorithm for the Graph Edit Distance problem (GED) on graphs of VC dimension $d$ running in time $n^{O(d/\varepsilon^{2})}$. In particular, this recovers a previous result by Arora, Frieze, and Kaplan [Math. Program. 2002] who gave an $\varepsilon n^{2}$-approximation running in time $n^{O(\log n/\varepsilon^{2})}$. Similar to the work of Arora et al., we extend our results to arbitrary Quadratic Assignment problems (QAPs) by introducing a notion of VC dimension for QAP instances, and giving an $\varepsilon n^{2}$-approximation for QAPs with bounded weights running in time $n^{O(\varepsilon^{-2}(d + \log\varepsilon^{-1}))}$. As a particularly interesting special case, we further study the problem $\varepsilon$-$\mathsf{GI}$, which entails determining if two graphs $G,H$ over $n$ vertices are isomorphic, when promised that if they are not, their graph edit distance is at least $\varepsilon n^{2}$. We show that the standard Weisfeiler--Leman algorithm of dimension $O(\varepsilon^{-1}d\log(\varepsilon^{-1}))$ solves this problem on graphs of VC dimension $d$. We also show that dimension $O(\varepsilon^{-1}\log n)$ suffices on arbitrary $n$-vertex graphs, while $k$-WL fails on instances at distance $\Omega(n^{2}/k)$.

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 presents an additive εn²-approximation algorithm for the Graph Edit Distance (GED) problem on n-vertex graphs of VC-dimension d, running in time n^{O(d/ε²)}. It recovers the Arora-Frieze-Kaplan result as the special case d=Θ(log n). The authors extend the approach to Quadratic Assignment Problems (QAPs) by defining an analogous VC-dimension parameter for QAP instances and obtain an εn²-approximation for bounded-weight QAPs in time n^{O(ε^{-2}(d + log ε^{-1}))}. As a special case they study the ε-GI promise problem and prove that the Weisfeiler-Leman algorithm of dimension O(ε^{-1}d log(ε^{-1})) solves it on VC-dimension-d graphs, while dimension O(ε^{-1} log n) suffices for arbitrary graphs and k-WL fails on instances at distance Ω(n²/k).

Significance. If the claimed runtime and approximation guarantees hold, the work improves the state of the art for structured instances of GED and QAP by replacing the log n factor with the (potentially much smaller) VC-dimension d. The ε-GI results give matching upper and lower bounds on the Weisfeiler-Leman dimension needed for robust isomorphism testing, directly relating combinatorial dimension to algorithmic complexity. The manuscript ships explicit algorithmic reductions to the Arora et al. framework together with new VC-dimension arguments for both graphs and QAPs.

major comments (2)
  1. [§3] §3 (or the section containing the main GED algorithm): the reduction from bounded-VC-dimension GED to the Arora-Frieze-Kaplan framework appears to rely on a sampling argument whose sample size is stated as O(d/ε²); a concrete bound on the failure probability and on how the VC-dimension controls the shattering of the sampled edit sets is needed to confirm that the overall runtime remains n^{O(d/ε²)} rather than incurring an extra log n factor.
  2. [QAP section] Definition of VC-dimension for QAP instances (the paragraph immediately preceding the QAP theorem): the definition is given only for bounded-weight instances; it is unclear whether the same parameter controls the approximation when weights are unbounded, and whether the stated runtime n^{O(ε^{-2}(d + log ε^{-1}))} continues to hold without the bounded-weight hypothesis.
minor comments (2)
  1. [ε-GI section] The statement of the ε-GI result for arbitrary graphs claims dimension O(ε^{-1} log n) suffices; the proof sketch should explicitly cite which theorem of Arora et al. is invoked and how the log n term arises from the general-case VC-dimension bound.
  2. [Throughout] Notation: the symbol d is overloaded for both graph VC-dimension and the QAP parameter; a brief remark distinguishing the two (or a subscript) would prevent confusion when the two results are read together.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful review and the recommendation of minor revision. We are pleased that the significance of the results on approximating GED and QAP for low VC-dimension instances, as well as the connections to Weisfeiler-Leman dimension, is recognized. We address the major comments below.

read point-by-point responses
  1. Referee: [§3] §3 (or the section containing the main GED algorithm): the reduction from bounded-VC-dimension GED to the Arora-Frieze-Kaplan framework appears to rely on a sampling argument whose sample size is stated as O(d/ε²); a concrete bound on the failure probability and on how the VC-dimension controls the shattering of the sampled edit sets is needed to confirm that the overall runtime remains n^{O(d/ε²)} rather than incurring an extra log n factor.

    Authors: We appreciate this observation. The sampling argument in Section 3 relies on the fact that the class of possible edit sets has VC-dimension at most d. By the standard uniform convergence bounds for VC-classes, a sample of size O(d/ε²) suffices to ensure that the empirical edit distance approximates the true value within additive ε n² with constant probability (at least 2/3), independently of n. There is no need for a failure probability that decreases with n, as the algorithm is Monte Carlo and a constant success probability is acceptable; repetitions to boost the probability incur only a polynomial factor in n, which is absorbed into the n^{O(d/ε²)} runtime bound. We will add this explicit reference to the VC uniform convergence theorem and the constant-probability analysis in the revised version to make the argument fully rigorous. revision: yes

  2. Referee: [QAP section] Definition of VC-dimension for QAP instances (the paragraph immediately preceding the QAP theorem): the definition is given only for bounded-weight instances; it is unclear whether the same parameter controls the approximation when weights are unbounded, and whether the stated runtime n^{O(ε^{-2}(d + log ε^{-1}))} continues to hold without the bounded-weight hypothesis.

    Authors: The VC-dimension for QAP instances is defined specifically for bounded-weight instances, as the subsequent theorem and runtime bound are stated under the bounded-weight hypothesis. For unbounded weights, the discretization step in the reduction does not apply directly, and the approximation may not hold with the same guarantees. We will revise the paragraph to explicitly state that the definition and results apply to bounded-weight QAPs, and add a remark clarifying that the bounded-weight assumption is necessary for our current techniques. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation self-contained

full rationale

The central results—an εn²-approximation for GED/QAP on VC-dimension-d graphs in time n^{O(d/ε²)}, plus WL-dimension bounds for ε-GI—build directly on the external Arora-Frieze-Kaplan algorithm and the standard Weisfeiler-Leman procedure. The VC-dimension parameter d enters the runtime as an explicit input hypothesis rather than a fitted or self-defined quantity. No equations reduce a claimed prediction to a prior fit by construction, no uniqueness theorem is imported from the authors' own prior work, and no ansatz is smuggled via self-citation. The abstract recovers the d=Θ(log n) case as a special instance of the new bound, confirming the argument is non-circular.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Review based on abstract only; full technical details unavailable. The central claims rest on the assumption that inputs have bounded VC-dimension and on the correctness of the Weisfeiler-Leman procedure.

axioms (1)
  • domain assumption Input graphs or QAP instances have bounded VC-dimension d
    Invoked to obtain the improved runtime; without it the algorithm reverts to slower bounds.

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