REVIEW 3 major objections 5 minor 33 references
A ZeNN architecture to avoid the Gaussian trap
T0 review · 3 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read A modified MLP architecture, Zeta Neural Networks, gives wide networks a pointwise-convergent, non-Gaussian infinite-width limit with a kernel that still depends on the parameters.
desk verdict A genuinely new wide-network architecture with sound convergence and non-Gaussian limit results, but the feature-learning claim outruns the proofs and the experiments are too thin to carry the practical weight. 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 ZeNN sum itself: enumerated perceptrons $p_{\hat\theta_j}(jx)=W_j^{(2)}\sigma\left(j W_j^{(1)} x + b_j^{(1)}\right)+b_j^{(2)}$, a non-learnable convergence weight $j^{-\alpha}$, and a frequency factor $j$ inside the activation. The key identity is cumulant additivity: for iid perceptrons, $\lambda^{(r)}_N(x)=\sum_{j=1}^N \lambda^{(r)}(jx)/j^{r\alpha}$, which at $x=0$ evaluates to $\lambda^{(r)}(0)$ times the Riemann zeta value $\zeta(r\alpha)$. This identity is what turns a divergence risk into a convergent, non-Gaussian limit, and the same weighted-sum structure carries through to the ZeNTK $K^N_\theta(x,y)$, whose second derivative with respect to a single output weight is nonzero on a full-measure set of parameters.
What would settle it
Take a ReLU perceptron with weight and bias distributions having a nonzero third cumulant at $x=0$, build $f^N_\theta(0)$ for growing $N$, and measure the standardized third cumulant; Theorem 2.2 predicts it converges to the nonzero constant $\lambda^{(3)}(0)\zeta(3\alpha)$, so a limit of zero (Gaussian behavior) would falsify the escape-from-the-Gaussian-trap claim. For the feature-learning claim, compute $K^\infty_\theta(x,y)$ at two nearby parameter values with $\dot\sigma\neq 0$ on an interval; if the values coincide, Theorem 2.5 fails.
Extended reading notes
Core claim
The paper's central claim is that replacing the averaged MLP sum $\frac{1}{N^\beta}\sum_j p_{\hat\theta_j}(x)$ by the weighted, frequency-scaled sum $f^N_\theta(x)=\sum_{j=0}^N j^{-\alpha}\left(W_j^{(2)}\sigma\left(W_j^{(1)}jx+b_j^{(1)}\right)+b_j^{(2)}\right)$ changes the infinite-width story completely. For continuous activations of at most polynomial growth $k$, and $\alpha>k+1$, the ZeNN sequence converges uniformly on compact sets and pointwise almost surely to an honest infinite series of perceptrons, so the limit is again a parametric network. Because the perceptrons are independent, the $r$-th cumulant of $f^N_\theta(x)$ is $\sum_j \lambda^{(r)}(jx)/j^{r\alpha}$; at $x=0$ this becomes $\lambda^{(r)}(0)\zeta(r\alpha)$, which does not vanish when a single perceptron has a nonzero cumulant of order at least three. The infinite-width distribution therefore retains non-Gaussian fingerprints of the initialization. Finally, the paper defines the ZeNTK and proves that, unlike the MLP neural tangent kernel, it is not a constant function of the parameters even in the $N\to\infty$ limit, which the paper equates with feature learning.
Load-bearing premise
That infinite-width ZeNNs perform feature learning is assumed to follow from the ZeNTK being a non-constant function of the parameters, an equivalence the paper does not derive; separately, the Schrödinger experiment's advantage depends on initializing the eigenvalue guess within about 1 of the true $k^2$.
Editorial extensions
If this is right
- Infinite-width ZeNNs are well-defined parametric models whose pointwise limit is an infinite series of scaled perceptrons, not a Gaussian field or the zero function.
- The limiting distribution records the initialization through all cumulants, so width does not erase architecture or initialization information.
- The ZeNTK depends on parameters even at infinite width, so ZeNNs do not fall into the fixed kernel regime that disables feature learning in MLPs.
- With sine-type activations, finite-width ZeNNs and their randoZeNN variant match or beat Fourier-feature baselines at fitting high-frequency functions of low-dimensional inputs.
- The Schrödinger PINN experiments indicate ZeNNs can find high-energy oscillatory eigenfunctions that standard MLPs miss, given a rough prior on the eigenvalue.
Reading between the lines
- The factor $j^{-\alpha}$ can be read as a tunable spectral prior: smaller $\alpha$ puts more weight on high-frequency neurons, and the paper's experiments use $\alpha=0$ or $\alpha=0.1$ when high frequencies matter, suggesting $\alpha$ controls a bias–variance trade-off across frequencies.
- Because the ZeNTK is parameter-dependent, ZeNN training dynamics are not linear in function space; this may change generalization and optimization behavior compared with NTK analysis, a testable consequence.
- The same enumerating-and-weighting trick could be applied to other basis-like architectures, as the paper's KAZeNN proposal hints, potentially taming their infinite-width limits too.
- The cumulant formula suggests ZeNNs could serve as controlled generators of non-Gaussian stochastic processes, with tail behavior tuned by $\alpha$ and the single-perceptron distribution.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Zeta Neural Networks (ZeNNs), defined as f_N^θ(x)=Σ_{j=1}^N j^{-α}(W_j^{(2)}σ(W_j^{(1)}jx+b_j^{(1)})+b_j^{(2)}), with α>0 a fixed convergence parameter. The main theoretical results are: (Theorem 2.1) for α>k+1 the finite-width ZeNN converges uniformly on compact sets and pointwise a.e. to an infinite series; (Theorem 2.2 and Remark 2.3) the limiting cumulants are Σ_j λ^{(r)}(jx)/j^{rα}, so the infinite-width limit is non-Gaussian when a single-perceptron cumulant of order ≥3 is nonzero; (Theorem 2.5) the ZeNTK is a non-constant function of parameters, which the paper interprets as feature learning in the infinite-width limit. The paper also proposes deep variants (oZeNN, radZeNN, randoZeNN, KAZeNN) and reports experiments on 1D regression, image regression, and PINN solutions of Schrödinger and sinc problems.
Significance. The construction is simple and the core theoretical computations are valuable: the pointwise-convergent series limit, the exact cumulant formula, and the closed-form ZeNTK are derived cleanly in Appendices A-C. If the feature-learning claim were established, the paper would offer a novel resolution of the Gaussian trap with a minimal architectural change. The paper is also honest in flagging its own limitations, notably the eigenvalue-initialization requirement in §4.3.1. However, the central feature-learning claim is currently supported only by parameter-dependence of the kernel, not by training dynamics, and the experimental evidence is not parameter-fair and lacks error bars or seeds. These gaps are load-bearing for the advertised contributions.
major comments (3)
- [§2, paragraph before Theorem 2.5; Theorem 2.5] The paper defines feature learning as 'the ability of changing the kernel through training' but Theorem 2.5 only proves that θ↦K^N_θ(x,y) and θ↦K^∞_θ(x,y) are non-constant as functions of θ. This is not sufficient: even finite-width MLPs have parameter-dependent NTKs, and the infinite-width MLP pathology is precisely that the kernel stops changing along the gradient-flow trajectory. The manuscript never computes d/dt K^N_{θ(t)} or its infinite-width limit; Appendix C derives the output dynamics (C.1) with K^N_θ treated as a fixed object. To support the abstract and §1.3 claim, the authors need to show that the kernel changes along the training trajectory (e.g., that the infinite-width limit of d/dt K^N_{θ(t)} is nonzero on a set of positive measure), or explicitly downgrade the claim to 'parameter-dependent infinite-width kernel' rather than 'feature learning.'
- [§4.3.1, Schrödinger experiment] The reported success at energy level n=10 relies on the initialization satisfying |k0^2 - k*^2| ≈ 1, i.e., a strong prior on the unknown eigenvalue; the text itself calls this 'clearly an undesirable feature.' As presented, this does not demonstrate an advantage of ZeNNs over MLPs under comparable prior knowledge, since the MLP baseline is not given the same information or a tuning procedure. At minimum, the authors should report the sensitivity of the method to k0 across a range of values and compare against MLP/FF baselines with similarly tuned initialization.
- [§4.1-4.2, experimental methodology] The empirical comparisons are not parameter-fair and no error bars, seeds, or run-to-run variability are reported. For instance, Figure 1 compares an MLP with 128 neurons trained for 50,000 epochs against a ZeNN with 64 neurons trained for 15,000 epochs, and §4.2 reports only the 'best performance we were able to achieve' after non-exhaustive hyperparameter search. Since the paper's practical claim ('ZeNNs excel at learning high-frequency features') is partly empirical, the authors should report mean and standard deviation over multiple seeds and match parameter counts or training budgets across architectures.
minor comments (5)
- [Definition 1.1] The sum runs from j=0 to N with factor 1/j^α, which is undefined at j=0; the theorems and proofs all start at j=1, so the definition should either start at j=1 or specify that the j=0 term is excluded.
- [Remark 2.3 vs Appendix B, Remark B.3] The main text says non-Gaussianity follows if a cumulant of order at least three is nonzero, but Remark B.3 says 'at least two.' The latter is inconsistent with the argument (the second cumulant is the variance and does not control Gaussianity).
- [Appendix D and §4.3] The first sentence of Appendix D says 'all such models' in a way that suggests it refers to Section 4.3, but the specifications are for the image-regression models of Section 4.2; this should be corrected for clarity.
- [References] Reference [10] lists the second author as 'G. Franck'; the correct name is Arthur Jacot, Franck Gabriel, and Clément Hongler. Also, the header of the paper contains 'A VOID' instead of 'AVOID' in the title.
- [Captions of Figures 6 and 7] The captions say 'sample points form the exact solution'; 'form' should be 'from.'
Circularity Check
No significant circularity: the central theorems are direct analytic consequences of the ZeNN definition; the only self-citation is non-load-bearing.
full rationale
ZeNNs are defined by f_N^theta(x) = sum_{j=0}^N j^{-alpha}(W_j^(2) sigma(W_j^(1) j x + b_j^(1)) + b_j^(2)). Theorem 2.1 is proved directly in Appendix A by bounding |sigma(jWx+b)| <= C(1 + j^k |W|^k |x|^k + |b|^k) and showing the j^{-alpha} j^k tail converges for alpha > k+1; no fitted quantity or external result is invoked. Theorem 2.2/B.1 derives the cumulant identity lambda_N^(r)(x) = sum_j lambda^(r)(jx) j^{-r alpha} from the iid structure and characteristic-function factorization; the non-Gaussian conclusion at x=0 follows because the cumulant series does not vanish, unlike the 1/sqrt(N) MLP scaling. Theorem 2.5/C.2 computes the second derivative of the ZeNTK with respect to W_j^(2) and shows the kernel and its N->infinity limit are non-constant in theta; this is a direct computation from the kernel definition. The inference from 'kernel non-constant' to 'feature learning' is the paper's explicitly adopted perspective ('it is this later perspective that we will adopt here', Section 1.1), not a hidden equivalence; the stronger claim that the kernel changes along the training trajectory is not established, but that is a correctness/evidential gap, not circularity. The only self-citation is reference [6] in the related-results survey of finite-width non-Gaussianity; the present proofs do not depend on it, so it is not load-bearing. Experimental alpha values are hyperparameters, not fitted parameters inside the derivations. The disclosed limitations in Section 4.3.1 (need |k0^2 - k*^2| approx 1) and Section 4.3.2 (sine-vs-sine criticism) are acknowledged weaknesses, not circular inferences. No equation reduces to its own input, and no fitted quantity is renamed as a prediction.
Assumptions & free parameters
free parameters (1)
- α (convergence parameter) =
1.1 in 1D regressions, 0.1 in PINNs, 0 in image regression
assumptions (3)
- domain assumption Activation functions have at most polynomial growth of order k
- domain assumption Parameter measures ν_j have uniformly bounded moments
- ad hoc to paper Feature learning is equivalent to the ZeNTK being non-constant in parameters
Cite this review
Pith. "Pith review of A ZeNN architecture to avoid the Gaussian trap." pith.science (2026). https://pith.science/paper/C3UDQT22
@misc{pith2026250520553,
author = {Pith},
title = {Pith review of: A ZeNN architecture to avoid the Gaussian trap},
year = {2026},
howpublished = {\url{https://pith.science/paper/C3UDQT22}},
note = {Machine review of arXiv:2505.20553}
}
read the original abstract
We propose a new simple architecture, Zeta Neural Networks (ZeNNs), in order to overcome several shortcomings of standard multi-layer perceptrons (MLPs). Namely, in the large width limit, MLPs are non-parametric, they do not have a well-defined pointwise limit, they lose non-Gaussian attributes and become unable to perform feature learning; moreover, finite width MLPs perform poorly in learning high frequencies. The new ZeNN architecture is inspired by three simple principles from harmonic analysis: i) Enumerate the perceptons and introduce a non-learnable weight to enforce convergence; ii) Introduce a scaling (or frequency) factor; iii) Choose activation functions that lead to near orthogonal systems. We will show that these ideas allow us to fix the referred shortcomings of MLPs. In fact, in the infinite width limit, ZeNNs converge pointwise, they exhibit a rich asymptotic structure beyond Gaussianity, and perform feature learning. Moreover, when appropriate activation functions are chosen, (finite width) ZeNNs excel at learning high-frequency features of functions with low dimensional domains.
Figures
Figures from the paper (4 more)
Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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