REVIEW 6 major objections 6 minor 43 references
This paper claims that a trainable, sigmoid-bounded weight between a Fourier-KAN branch and an MLP branch, combined with overlapping domain decomposition, lets a physics-informed neural network solve high-frequency and multiscale PDEs more
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-03 22:14 UTC pith:ACKYLOZR
load-bearing objection Trainable sigmoid-bounded MLP/KAN weight is a plausible idea, but the paper never compares it to fixed-α tuning, and its cost claims contradict its own conclusion. the 6 major comments →
The modified Physics-Informed Hybrid Parallel Kolmogorov--Arnold and Multilayer Perceptron Architecture with domain decomposition
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
On the paper's own terms, the discovery is that replacing the fixed hyperparameter alpha in the hybrid parallel KAN–MLP architecture with a trainable parameter constrained by S(alpha) in [0,1] yields a self-balancing network: as training proceeds, S(alpha) moves toward the MLP for low-frequency problems and toward the KAN for high-frequency problems. Combined with overlapping domain decomposition and hard-constrained boundary and initial conditions, this modified HPKM-PINN reproduces oscillatory solutions such as sin(32πx)sin(32πy), and in Table 1 it reports the best L2 error among the three architectures on every benchmark considered — for example, Helmholtz with ω=48 at 8.698e-4 versus 1.1
What carries the argument
The central object is the modified HPKM output u = S(α) u_KAN + (1 − S(α)) u_MLP, where u_KAN is a Fourier-KAN (a Kolmogorov–Arnold network whose univariate activations are truncated Fourier series) and u_MLP is a standard multilayer perceptron. S is an S-shaped map (sigmoid in the final experiments) that confines α to [0,1]; in the domain-decomposed version each subdomain has its own α^(i), and a partition-of-unity window function ω_i blends the local modified-HPKM outputs into a global solution. The mechanism doing the work is the adaptive convex gate: it is trained jointly with the network weights by gradient descent, so the model can tilt toward whichever branch fits the local frequency
Load-bearing premise
The load-bearing premise is that one scalar weight, squeezed into [0,1], can keep the KAN and MLP branches cooperating so the KAN supplies high frequencies and the MLP supplies low frequencies; if the two branches interfere instead of complementing, the reported advantages could depend on the specific benchmark settings.
What would settle it
On the high-frequency Helmholtz case (ω=32), record the trained S(α) over many seeds: the paper's mechanism predicts it drifts toward 1, favoring KAN, and that this drift is what produces the accuracy gain. A concrete falsifier is to freeze S(α) at 0.5 and rerun the same benchmarks: if accuracy does not degrade materially, the trainable gate is not the active ingredient. A second check is to replace the Fourier basis in the KAN branch with a static nonlinearity while retraining; if the final L2 errors are statistically unchanged, then the high-frequency claim is not being driven by the Fourier
If this is right
- The mixing ratio between KAN and MLP no longer needs manual grid search; training sets it, and the S-shaped bound keeps it a valid convex combination.
- On the reported benchmarks, the hybrid delivers smaller L2 error than either single-branch architecture under matched domain decomposition, so it can be read as a more accurate default for oscillatory PDEs.
- Because the hybrid matches or beats 32-neuron baselines with 16 neurons per branch, the parameter count and memory footprint are smaller than a pure KAN of comparable width.
- Input normalization inside each overlapping subdomain converts global high-frequency features into local lower-frequency ones, which the paper identifies as the reason spectral bias is mitigated.
- The evolution of S(α) gives a diagnostic: the learned gate tilts to MLP on low-frequency problems and to KAN on high-frequency problems, supporting the frequency-separation narrative.
Where Pith is reading between the lines
- Editorial inference: If the learned S(α) is the mechanism, then the same gate idea could be applied at the level of loss terms or frequency bands rather than only subdomains; the paper provides no test of whether per-subdomain weights are essential or merely convenient.
- Editorial inference: The paper's benchmark list is separable and low-dimensional; whether the 16-neuron hybrid retains its advantage on non-separable, three-dimensional, or time-critical problems is an untested extrapolation.
- Editorial inference: The reaction-diffusion result, where MLP and KAN both fail at about 0.92 while the hybrid reaches 1e-4, suggests the two branches' errors are not just averaged but cancel or complement; a controlled study varying branch widths could show whether the benefit is from the gate or from having two different inductive biases at all.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a modified Hybrid Parallel Kolmogorov–Arnold Network and Multilayer Perceptron PINN (modified HPKM-PINN) with overlapping domain decomposition. The key modification is replacing the fixed weighting parameter α in the HPKM combination with a trainable parameter transformed by an S-shaped function, so that the convex combination of KAN and MLP outputs is adaptively balanced. The method is tested on Helmholtz (ω=16,32,48), 2D and 5D Poisson, reaction–diffusion, and Allen–Cahn benchmarks, reporting lower L2 errors than MLP-only and KAN-only PINNs. The abstract claims that the method reduces training costs and improves computational efficiency compared with manual hyperparameter tuning.
Significance. If substantiated, the contribution is a simple and inexpensive architectural modification with a plausible intuitive appeal: combining a KAN branch and an MLP branch with a bounded trainable weight within an overlapping domain decomposition. The benchmark suite is reasonably broad, including high-frequency and multiscale problems, and the method is easy to implement. However, the central efficiency claim is unsupported and is in direct tension with the paper's own conclusion that the model requires higher training costs than MLP architectures. The experiments do not isolate the effect of the adaptive weighting mechanism, report no statistical uncertainty, and provide no code. The frequency-separation narrative is also not established. The paper therefore presents a promising empirical idea that requires substantially stronger validation, rather than a demonstrated method.
major comments (6)
- [§3.1.1, Eq. (2.2)] The central novelty is the trainable weighting parameter S(α). The experiments in Figs. 4–7 compare only different S-shaped functions and the unweighted 'No α' direct sum; they do not include any fixed-α baseline (e.g., α=0, 0.25, 0.5, 0.75, 1) or the original HPKM with manually tuned α. Since the abstract claims reduced cost compared with manual hyperparameter tuning, this missing control is load-bearing. The reported gains could come from the hybrid architecture itself or the domain decomposition rather than from the adaptive mechanism. Add fixed-α baselines and report the cost of tuning α.
- [§4 vs. Abstract] The conclusion states that the model 'requires higher training costs than traditional MLP architectures due to its larger parameter size,' while the abstract claims the method 'reduces training costs and improves computational efficiency compared with manual hyperparameter tuning.' No runtime, FLOPs, or parameter counts are reported anywhere. The efficiency claim is therefore unsupported and internally inconsistent. The authors should either substantiate the claim with measurements or remove it from the abstract and introduction.
- [§3.1, §3.2.1, §3.3, §3.4] Overlap ratios, subdomain counts, sampling points, Fourier frequency count K, hard-constraint steepness σ, and the choice of S-shaped function are selected per benchmark with statements such as 'Based on our tests' and 'determined through testing.' The sigmoid function is selected after comparing candidates on the same Helmholtz problems that are later used to claim superiority. This is selection on the test problems and risks circularity. The authors should provide sensitivity analyses and make it clear that all baselines were tuned with the same effort, or conduct validation on separate problems.
- [§2.2.2, Algorithm 1] The hard-constraint operator C is not defined in general. An explicit tanh-based construction is given only for the Helmholtz equation; for the Poisson, reaction–diffusion, and Allen–Cahn examples no hard-constraint construction is provided, even though all experiments rely on it. This omission prevents reproduction. Provide the concrete form of C for each benchmark or switch to soft constraints with reported loss weights.
- [§2.1.2, Figs. 5 and 7] The paper claims that a single scalar S(α) automatically balances low-frequency (MLP) and high-frequency (KAN) components. However, both branches receive identical inputs and S(α) is a global scalar per subdomain, not a frequency-dependent filter. The observed improvements may instead reflect an ensemble effect or the higher capacity of having two branches. The S(α) trajectory plots do not demonstrate frequency separation. Please provide a concrete analysis of when the two branches interfere or soften the interpretation.
- [Table 1] All L2 errors in Table 1 are single-run numbers with no seeds, no error bars, and no code. Neural network training is stochastic, so differences such as 2.362×10⁻⁴ vs. 5.115×10⁻⁴ may lie within run-to-run variability. The manuscript should report means and standard deviations over multiple seeds and, ideally, release code to make the comparisons reproducible.
minor comments (6)
- [§3.1 title] Typo: 'Hemholtz' should be 'Helmholtz'.
- [§3.1.2] Typo: 'KAN-baed model' should be 'KAN-based model'.
- [Fig. 9 caption] Typo: 'Possion' should be 'Poisson'.
- [References [16]–[17]] The KAN citation is inconsistent: the introduction refers to 'Li et al. [17]' but reference [17] is Kodama (2011); the KAN paper appears as reference [16] with different authors. Reference [6] is cited for a lack of theoretical analysis but actually points to a Fourier features paper.
- [Eq. (3.7)] The definition of f(x) has unbalanced parentheses, which should be corrected.
- [Algorithm 1] Line 14 says 'Hard constraints: û^(i)=C u^(i)' but the operator C is not specified there; please clarify that it refers to the construction in §2.2.2 and give the explicit form.
Circularity Check
No circularity found: architecture is defined by Eq. (2.2) and compared on benchmarks; noted weaknesses are experimental-support issues, not derivation-by-construction circularity.
full rationale
The paper's claimed contribution is a trainable weighting S(α) inserted in Eq. (2.2); S(α) is a trainable parameter, not fitted to the reported benchmark outputs. No equation in Section 2 reduces to another by construction: Eq. (2.3) is the definition of the network output, and Eq. (2.4) is the standard PINN loss. The HPKM architecture is attributed to external prior work [37], Fourier KAN to [36], and FBPINN domain decomposition to [30,32,38]; none of these are self-citations of the present authors, and none is used to forbid alternatives. The main weaknesses—the sigmoid function and overlap ratios selected on the same Helmholtz/Poisson benchmarks later reported, and the conclusion conceding higher training cost than MLP ('Although the model requires higher training costs than traditional MLP architectures...')—undercut the abstract's cost-saving claim, but they are experimental-support and consistency issues, not circular reductions. Therefore no significant circularity is found.
Axiom & Free-Parameter Ledger
free parameters (8)
- Overlap ratio δ =
3.3 (Helmholtz); 2.9 (2D Poisson, reaction-diffusion, Allen-Cahn); 1.9 (5D Poisson)
- Number of subdomains N =
20×20 for Helmholtz and Allen-Cahn; 2^(m-1)×2^(m-1) for 2D Poisson; 2^5 for 5D Poisson; 10 for reaction-diffusion
- Sampling point counts =
260×260 (Helmholtz, Allen-Cahn); (10·2^(m-1))² (2D Poisson); 10^5 (5D Poisson); 200 (reaction-diffusion)
- S-shaped weighting function S(α) =
sigmoid
- Fourier KAN frequency count K =
4
- Hard-constraint steepness σ =
0.2 (Helmholtz)
- Network width =
16 neurons per layer for modified HPKM; 32 for MLP and KAN baselines
- Learning rate =
1e-4 (Adam)
axioms (6)
- standard math Kolmogorov-Arnold representation theorem, and the KAN approximation built on it
- domain assumption Minimizing the PINN residual with hard-constrained boundary/initial terms yields the PDE solution
- domain assumption Partition-of-unity window functions produce a valid continuous global solution from local subnetworks
- domain assumption Input normalization inside each subdomain lowers effective frequency and mitigates spectral bias
- domain assumption Fourier-KAN basis functions approximate high-frequency components better than B-spline KAN or MLP
- ad hoc to paper A bounded convex combination S(α)∈[0,1] improves optimization stability
read the original abstract
In this work, we propose a modified Hybrid Parallel Kolmogorov--Arnold Network and Multilayer Perceptron Physics-Informed Neural Network to overcome the high-frequency and multiscale challenges inherent in Physics-Informed Neural Networks. This proposed model features a trainable weighting parameter to optimize the convex combination of outputs from the Kolmogorov--Arnold Network and the Multilayer Perceptron, thus maximizing the networks' capabilities to capture different frequency components. Furthermore, we adopt an overlapping domain decomposition technique to decompose complex problems into subproblems, which alleviates the challenge of global optimization. Benchmark results demonstrate that our method reduces training costs and improves computational efficiency compared with manual hyperparameter tuning in solving high-frequency multiscale problems.
Figures
Reference graph
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