REVIEW 3 major objections 4 minor 1 cited by
Granger Causality Detection with Kolmogorov-Arnold Networks
T0 review · 3 major / 4 minor · reviewed 2026-08-11 · deepseek-v4-flash
Pith's one-line read Kolmogorov-Arnold networks, with learnable spline edge functions and a first-layer proximal threshold, can match or slightly beat multilayer perceptrons at detecting sparse Granger causal relationships in time series.
desk verdict GC-KAN is a sensible combination of KANs and component-wise neural Granger causality, with a clean proximal sparsity trick that does produce exact zeros, but the paper's central claim that KANs outperform MLPs is not supported by the current evaluation—the cMLP baselines are borrowed from another paper under different conditions, and Eq. 18 is underspecified. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The carrying object is the KAN's first edge layer, $\Phi_0 = W_{\mathrm{base}}\sigma(z) + W_{\mathrm{spline}}\,\mathrm{spline}(z)$, where each connection is a learnable B-spline function rather than a scalar weight. Causality is extracted from this layer by summing the magnitudes of the first-layer functions that map each lagged input to each hidden neuron, and the proximal update $w \leftarrow \operatorname{sign}(w)\max(|w|-\eta\lambda_{\mathrm{prox}},0)$ is applied only to $W_{\mathrm{base}}$ and $W_{\mathrm{spline}}$ so that weak functions become exactly zero. The L1 and entropy penalties on the whole layer encourage sparse and balanced use of the splines, and the deliberately small architectures (one or ten hidden neurons) keep the resulting causal map readable. The mechanism converts the question 'does series $j$ Granger-cause series $i$?' into 'does the corresponding first-layer spline contribution survive proximal thresholding?'
What would settle it
Train a GC-KAN on the paper's VAR(1) data and recompute $C_{j,k}$ with two natural definitions of $|\varphi|$, such as the $L^2$ norm over the training inputs and the $\ell^1$ norm of the B-spline coefficients; if the two rankings of candidate parents disagree, the causal extraction rule is not well-defined.
Extended reading notes
Core claim
The central claim is that replacing the scalar input weights of a component-wise neural Granger model with KAN's learnable spline functions, and adding a proximal operator that soft-thresholds only the first-layer functions, yields a Granger causality detector that is at least as accurate as the established MLP baseline and more directly interpretable. Concretely, the paper defines GC-KAN, in which each target series is modeled by a KAN fed with all lagged series, and after training the Granger contribution of lag $k$ of series $j$ is read off as $C_{j,k}=\sum_{i=1}^{n_{\text{hidden}}}|\varphi_{j,k,i}|$. Because the proximal step forces irrelevant first-layer functions to exact zero, causal parents can be identified from the nonzero contributions without manual thresholding. In experiments, GC-KAN's AUROC is comparable to cMLP with hierarchical group lasso, with the largest reported margins on VAR(1) and VAR(2) at $T=1000$ and on Lorenz-96 with forcing $F=10$ at $T=250$.
Load-bearing premise
The load-bearing premise is that every first-layer spline function has a well-defined magnitude so that the contribution score $C_{j,k}$ in Eq.~18 can be computed; the paper never states how the magnitude of a spline function is measured.
Editorial extensions
If this is right
- GC-KAN with a single hidden neuron matches or beats cMLP with 100 hidden neurons on VAR data at $T=500$ and $T=1000$, so KAN-based detection can be much more parameter-efficient.
- Because the proximal step zeros out irrelevant inputs, GC-KAN can produce a Granger causality matrix directly from the trained network, without a manual pruning threshold.
- On Lorenz-96 with $F=10$ and $T=250$, GC-KAN slightly outperforms cMLP, suggesting spline activations help in low-sample nonlinear regimes.
- If the pattern holds, KAN-based frameworks are a viable route for causal discovery in high-dimensional physical and economic time series.
Reading between the lines
- The paper's contribution score assumes a well-defined magnitude for each spline function $\varphi_{j,k,i}$, but no norm is specified; choosing different natural norms, such as the $L^2$ norm over inputs or the $\ell^1$ norm of B-spline coefficients, could change the ranking of candidate causal parents.
- A natural follow-up is to group lags of the same variable inside GC-KAN, mirroring the hierarchical group lasso, which would add automatic lag-order selection to the spline-based detector.
- The authors' suggestion that KANs can fit symbolic functions implies a concrete next step: converting each surviving first-layer spline into an explicit symbolic expression, which would turn GC-KAN into a dynamical-law extractor rather than only a causal detector.
- The reported advantages appear mainly in compact architectures, so an equal-parameter comparison, rather than equal-neuron comparison, would clarify whether the gain comes from spline flexibility or from model size.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces GC-KAN, a Kolmogorov-Arnold network based framework for nonlinear Granger causality detection. Each target time series is modeled by a KAN whose first-layer spline activations map lagged inputs to hidden neurons; sparsity is encouraged by L1 and entropy regularization plus a proximal soft-thresholding step applied to the first layer. The method is evaluated on synthetic VAR(1), VAR(2), and Lorenz-96 data with known ground truth, and AUROC scores are compared with cMLP results taken from Tank et al. [15]. The authors report comparable or slightly better accuracy for GC-KAN in several settings and argue that KANs offer a more parameter-efficient and interpretable alternative to MLPs for sparse high-dimensional Granger causality detection.
Significance. If the central claim were fully supported, the paper would make a useful contribution by adapting KANs to nonlinear Granger causality with an explicit sparsification mechanism and a compact architecture. The proximal-operator idea is a sensible adaptation of the cMLP pipeline to spline-based networks, and evaluating on synthetic systems with known ground truth is appropriate. The manuscript is also honest in reporting that many differences are small. However, the evidence for the headline claim that GC-KAN can outperform MLPs is weakened by an unequal benchmark: cMLP results are borrowed from [15] with a 100-hidden-neuron architecture and a different data pipeline, while GC-KAN results are generated in-house with 1 or 10 hidden neurons. In addition, the causal contribution metric in Eq. (18) is not fully specified because the norm of a spline function is not defined. A matched-condition rerun and a precise definition of the contribution score would be needed before the comparative claim can be accepted.
major comments (3)
- [Section III, Tables I and II] The headline comparison is not made on equal footing. The cMLP AUROC values are "taken directly from [15]" and correspond to a 100-hidden-neuron cMLP optimized with Hierarchical Group Lasso on data from a different pipeline, whereas the GC-KAN results are produced by the authors with 1 (VAR) or 10 (Lorenz-96) hidden neurons on their own simulated data. The reported margins (e.g., 99.3 vs 98.4 at T=1000 in VAR(1), and 95.7 vs 95.5 at T=1000, F=40 in Lorenz-96) are small, and no matched-condition standard deviations are provided for the borrowed baseline. Consequently, the central claim that GC-KAN has the potential to outperform MLPs in Granger causality detection is not supported by controlled evidence; the authors should rerun cMLP under identical data, preprocessing, and capacity settings.
- [Eq. (18) in Section II.C.2] The Granger contribution C_{j,k} is defined as a sum of |φ_{j,k,i}|, but φ_{j,k,i} is a learnable spline function, not a scalar. The paper never states whether the absolute value refers to the L1 norm defined in Eq. (11), the absolute value evaluated at a particular input, or some other functional norm. Since this quantity is used to construct the binary Granger causality matrix that underlies the ROC curves, the causal scoring rule is not mathematically specified and the experiments are not reproducible as written. Please define the norm explicitly.
- [Section IV and Table II] The conclusion that GC-KAN shows "stronger performances in low-sample-size settings" for Lorenz-96 is overstated. At F=10, T=250 the AUROC values are 86.9±0.5 for GC-KAN versus 86.6±0.2 for cMLP, which is within the reported standard deviations; the only non-overlapping low-sample advantage appears at F=40, T=250 (86.3±0.2 vs 84.0±0.5). The claim should be qualified to refer to that specific setting.
minor comments (4)
- [Section III.B] The phrase "10 add hidden neurons" should read "10 additional hidden neurons."
- [Fig. 1 caption] The caption states that the data are generated from an n=10 VAR(3) model, while Section III.A describes the VAR experiments as n=20 VAR(1) and VAR(2). This inconsistency should be resolved.
- [Eq. (14)] The GC-KAN loss omits the summation over time steps t=p,...,T that appears in the cMLP loss of Eq. (5). Please make the notation consistent.
- [Eqs. (16)-(17)] The proximal operator is written as Prox_{λprox}, but the soft-thresholding rule uses ηλprox as the threshold. The role of the learning rate η in the definition of the proximal map should be clarified.
Circularity Check
No significant circularity: the method is validated against known synthetic ground truth, and the cited baselines and KAN machinery are external prior work rather than self-citations that smuggle in the conclusion.
full rationale
The paper's central claim is that GC-KAN can detect Granger causality and can be competitive with or outperform cMLP. The evaluation is conducted on synthetic VAR and Lorenz-96 data with known ground-truth causal structure, and the reported AUROC numbers are computed by sweeping the proximal/sparsity strength and comparing against that ground truth. No parameter is fitted to the target causal matrix, and no prediction reduces to an input by construction. The KAN formulation (Eq. 7-14), the proximal operator (Eq. 16-17), and the causal contribution metric (Eq. 18) are all stated as algorithmic definitions rather than results derived from an assumed conclusion. The only notable weakness is that cMLP results are 'taken directly from [15]' (Tables I and II), which raises a benchmarking-fairness concern because the cMLP baseline was trained under different architecture choices and data draws than the GC-KAN runs. That is an experimental validity issue, not a circularity issue: the cMLP numbers are external evidence, not a fitted constant from this paper. Similarly, Eq. 18 is notationally underspecified because phi is a spline function and the paper does not explicitly say it is using the |phi|_1 norm of Eq. 11, but ambiguity is a reproducibility defect, not a self-referential reduction. There are no load-bearing self-citations by the present authors, no uniqueness theorem imported from their own prior work, and no ansatz smuggled in via their own citations. The honest finding is therefore no significant circularity, score 0.
Assumptions & free parameters
free parameters (5)
- proximal strength λ_prox =
swept over a range
- regularization weight λ =
not specified (μ1=μ2=1)
- number of hidden neurons =
1 for VAR, 10 for Lorenz-96
- max lag p =
5
- spline grid size and order =
not specified
assumptions (3)
- standard math Kolmogorov-Arnold representation theorem ensures KANs can represent any continuous multivariate function
- domain assumption The simulated VAR and Lorenz-96 data satisfy the Granger causality assumptions, including stationarity, no unobserved confounders, and a complete system
- ad hoc to paper Ten hidden neurons are sufficient to capture Lorenz-96 nonlinearities via the identity 2xy = (x+y)^2 - (x^2 + y^2)
Cite this review
Pith. "Pith review of Granger Causality Detection with Kolmogorov-Arnold Networks." pith.science (2026). https://pith.science/paper/V5C2GW6A
@misc{pith2026241215373,
author = {Pith},
title = {Pith review of: Granger Causality Detection with Kolmogorov-Arnold Networks},
year = {2026},
howpublished = {\url{https://pith.science/paper/V5C2GW6A}},
note = {Machine review of arXiv:2412.15373}
}
read the original abstract
Discovering causal relationships in time series data is central in many scientific areas, ranging from economics to climate science. Granger causality is a powerful tool for causality detection. However, its original formulation is limited by its linear form and only recently nonlinear machine-learning generalizations have been introduced. This study contributes to the definition of neural Granger causality models by investigating the application of Kolmogorov-Arnold networks (KANs) in Granger causality detection and comparing their capabilities against multilayer perceptrons (MLP). In this work, we develop a framework called Granger Causality KAN (GC-KAN) along with a tailored training approach designed specifically for Granger causality detection. We test this framework on both Vector Autoregressive (VAR) models and chaotic Lorenz-96 systems, analysing the ability of KANs to sparsify input features by identifying Granger causal relationships, providing a concise yet accurate model for Granger causality detection. Our findings show the potential of KANs to outperform MLPs in discerning interpretable Granger causal relationships, particularly for the ability of identifying sparse Granger causality patterns in high-dimensional settings, and more generally, the potential of AI in causality discovery for the dynamical laws in physical systems.
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introduced the component-wise Multilayer Percep- tron (cMLP) and the component-wise Long Short-Term ∗ Corresponding author Email address: hongyu.lin.18@ucl.ac.uk Memory network (cLSTM) for multivariate nonlinear Granger causality. In these approaches, each target time series is independently modeled using a dedicated MLP or LSTM, with the lagged values of...
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Mathematical Formulation for GC-KAN The GC-KAN model consists of one KAN for each time series in the multivariate system xt. Each KAN is tasked with predicting a single target series xt,i based on the lagged observations of all series. The input vector for each GC-KAN is defined as: z = [xt−1, xt−2, . . . ,xt−p] ∈ Rnp×1. The output of each KAN is the pred...
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GC-KAN Optimization for Granger Causality The first layer of GC-KAN maps time-lagged inputs to hidden representations. Granger causality is extracted from the functional mappings in the first layer, which en- code the contribution of each lagged input series to the prediction of the target series. By analyzing these map- pings, significant contributions c...
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