REVIEW 4 major objections 4 minor 26 references
Fixed Aggregation Features Can Rival GNNs
T0 review · 4 major / 4 minor · reviewed 2026-08-03 · deepseek-v4-flash
Pith's one-line read Fixed neighborhood statistics plus a tuned MLP rival trained GNNs on 12 of 14 node-classification benchmarks.
desk verdict Useful, carefully-done baseline paper whose headline overclaims: Table 1 gives 10/14, not 12/14, and the transformer comparison is inherited, not run. 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
Fixed Aggregation Features (FAFs): a node's representation is built by applying non-learned permutation-invariant reducers (mean, sum, max, min, std) to feature multisets of neighbors at each hop k=1..K, concatenating all hops with the node's original features, and training an MLP on the resulting table. The theoretical backstop is a sum-aggregation injectivity theorem for orthogonal features at hop 1 and a Kolmogorov-Arnold-based discontinuous encoding Φ that is lossless but ill-conditioned; the practical work is done by hop-concatenation and a well-tuned nonlinear readout.
What would settle it
A concrete falsification would be a node-classification benchmark—real or synthetic—where labels depend on neighborhood structure that is not recoverable from these reducers at any hop, yet a trained GNN succeeds while FAFs fail. For example, a task where the label depends on the exact multiset of neighbor labels at hop 3 with non-orthogonal features, or on whether two specific neighbors share a common neighbor; if a tuned GNN solves it and FAF+MLP cannot, the paper's generalization claim would fail.
Extended reading notes
Core claim
The central claim is that a fixed, parameter-free aggregation of node features over neighborhoods—followed by a well-tuned MLP—can match or exceed state-of-the-art GNNs and graph transformers on 12 of 14 node-classification benchmarks. The exceptions are two heterophilous tasks (Roman-Empire and Minesweeper) that appear to need longer-range, hop-specific signal that simple reducers fail to capture. The paper further proves that 1-hop sum aggregation is injective on orthogonal features, and that a discontinuous Kolmogorov-Arnold encoding is lossless in principle yet numerically brittle in practice. The conclusion is that on most current benchmarks, learned aggregation is not the source of GNN
Load-bearing premise
The central practical claim rests on the assumption that concatenating simple distribution-only reducers (mean, sum, max, min) over a few hops preserves the task-relevant neighborhood information on these benchmarks; the paper proves this only for sum on orthogonal features at one hop, and its lossless Kolmogorov-Arnold encoding is too numerically brittle to use.
Editorial extensions
If this is right
- A tuned FAF baseline should be included in any node-classification benchmark to calibrate what fixed aggregation alone achieves.
- Datasets where FAFs reach state-of-the-art should be re-evaluated or retired as tests of learned message passing.
- The ablations show that concatenating all hops and using an MLP rather than a linear readout are key to matching GNNs.
- On most benchmarks, two hops suffice, implying that long-range aggregation is not driving current results.
- Benchmark design should shift toward tasks where relevant signal genuinely lies at distant hops and requires learnable aggregation.
Reading between the lines
- If FAFs match GNNs on these benchmarks, then reported accuracy gains of new graph architectures on the same datasets are more plausibly attributed to hyperparameter tuning, optimization, or classifier architecture than to learned aggregation; this is a testable re-evaluation, not the paper's own claim.
- A natural extension is to swap the MLP for gradient-boosted trees or other tabular learners on FAF features; the paper hints at this but does not test it, and gains could be dataset-dependent.
- The SHAP-based feature attribution offered by FAFs could be used prospectively to pre-screen datasets: if early-hop mean features separate classes well, a dataset is unlikely to reward GNN-specific inductive biases.
- The two failing datasets suggest a concrete research target: characterize the precise long-range or inter-hop statistics that simple reducers miss, and design a fixed reducer that captures them.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes Fixed Aggregation Features (FAFs): for each node, the original feature vector is concatenated with fixed, untrained multi-hop aggregations of neighbor features (mean, sum, max, min, std, optionally combined), and the resulting table is fed into a tuned MLP for node classification. The authors argue that learned neighborhood aggregation is not necessary on most standard benchmarks, support this with a theory section (injectivity of sum on orthogonal features, and a Kolmogorov–Arnold lossless encoding), and report experiments on 14 datasets comparing FAF+MLP with classic GNNs (GCN, GAT, GraphSAGE) and, via numbers inherited from Luo et al. (2024), with graph transformers and heterophily-aware models. The headline claim is that FAFs rival or outperform these models on 12/14 tasks, with Roman-Empire and Minesweeper as the only exceptions. The manuscript also provides ablations over hops, reducers, classifier depth, and running time, plus a comparison with GESN and preliminary results on GraphLand.
Significance. If the empirical claim were fully supported, this would be a useful contribution: a strong, interpretable, fixed-feature baseline for node classification, with practical implications for benchmark design and for what aspects of GNNs are actually load-bearing. The paper has real strengths: the code is public, the per-variant and per-hop tables are detailed, validation/test splits are reported, and the ablations (Tables 6–10) are informative. However, the central '12/14' claim is contradicted by the paper's own Table 1, and the comparison to graph transformers is inherited rather than run in this manuscript. After correcting these issues, the core idea still has value as a strong tabular baseline, but the paper's current framing substantially overstates the evidence.
major comments (4)
- [Abstract, Section 5, Table 1] The abstract and introduction state that FAFs rival or outperform GNNs and graph transformers on 12/14 tasks, with only Roman-Empire and Minesweeper as exceptions. This is not supported by Table 1. Section 5 itself says FAFs 'improve on 5 datasets, match within error or 1% on another 5, and trail on 4.' The four trailing datasets are Citeseer (FAFbestval 70.48±1.24 vs GCN 72.72±0.45), Cora (82.84±0.63 vs GCN 84.38±0.81), Minesweeper (90.00±0.39 vs SAGE 97.72±0.70), and Roman-Empire (78.11±0.38 vs GCN 91.05±0.15). The Citeseer and Cora gaps exceed 1.5 points and do not overlap within standard errors, so they cannot be called 'close to parity' under the paper's own 1% criterion. The data support at most 10–11/14 for classic GNNs, not 12/14. This is a load-bearing inconsistency in the headline contribution and must be corrected by revising the counts and the list of exceptions.
- [Section 5, Table 1, Abstract] The abstract claims FAFs rival or outperform 'state-of-the-art GNNs and graph transformers,' but Table 1 and Section 5 only report experiments against GCN, GAT, and GraphSAGE. No graph transformer is run in this paper; the comparison to graph transformers and heterophily-aware models is inherited from Luo et al. (2024). No table reproduces those numbers or shows how FAFs compare with them. If the authors wish to retain the graph-transformer claim, they need to either run those models under the same protocol or explicitly restrict the claim to classic GNNs and cite the inherited results only as context. As written, the abstract's scope is not substantiated by the experiments.
- [Section 4, Theorem 4.1, Introduction] The theoretical justification for why simple reducers suffice is limited. Theorem 4.1 proves injectivity of sum aggregation only under the assumption that node features are orthogonal (and finite in number). The paper's introduction states that 'on hops 0–1, sum and mean preserve information' without this qualification, and the benchmark datasets have dense or bag-of-words features that are not orthogonal. The paper acknowledges information loss for k≥2 but still uses this theory as the main explanation for FAFs' empirical success. The claims in the introduction and Section 4 should be explicitly conditioned on the orthogonality assumption, and the text should clarify that the theorem is a proof of possibility under idealized features, not an explanation for the observed performance on non-orthogonal real-world features.
- [Appendix D, Table 11] The Kolmogorov–Arnold (KA) reducer is described as theoretically lossless, but the implementation for multisets is not permutation-invariant: 'we make it act on multisets by sorting, which we fix by the given data order' (Appendix D). Node ordering is arbitrary, so this is not a well-defined function on multisets; two isomorphic neighborhoods with different orderings would produce different features. The poor results in Table 11 (e.g., Cora training accuracy 14.29±0.00, which is exactly chance for 7 classes) may reflect this implementation choice rather than the intrinsic brittleness of Φ. Please either provide a canonical permutation-invariant construction or clearly state that the KA experiment is a non-invariant heuristic and not a test of Theorem 4.2.
minor comments (4)
- [Abstract, Section 3] 'Training-free approach' is potentially misleading because the aggregation is training-free but the downstream MLP is trained. Consider rewording to 'training-free aggregation' or 'fixed aggregation'.
- [Section 5, Table 5/6] The paper selects 'FAFbestval' from validation across several variants. Please state explicitly how many variants were considered for each dataset and whether the same validation split was used for all variants, so readers can assess potential selection bias.
- [Figure 3, Appendix A.1] The panels in Figure 3 are dense and the axes in panels (a.iii), (b.i), and (c.ii) are not all labeled. Adding labels and a short walk-through would make the visualization of Φ and its inverse much easier to follow.
- [Table 4, Appendix B] The table caption does not define the columns 'hop' and 'mlp layers' for FAF; adding a sentence clarifying that 'hops' is the aggregation depth K and 'mlp layers' is the number of hidden layers would improve readability.
Circularity Check
No significant circularity: FAFs are independently defined fixed aggregations, the theory imports external theorems, and the empirical comparisons are standard train/validation/test evaluations.
full rationale
The central construction (Eqs. 1–2) defines FAFs as concatenations of fixed reducers (mean, sum, max, min, std) over hops; no target quantity is used to define the features. The MLP classifier is trained on training labels and the best FAF variant is chosen by validation (Table 5) and then reported on test (Table 6), which is standard model selection, not a fitted parameter being renamed as a prediction. The theoretical claims are imported from external work: Theorem 4.1 generalizes Lemma 5 of Xu et al. (2019) and is proved in Appendix A.2 via explicit extraction of counts from orthogonal-feature sums; Theorem 4.2 is Theorem 2 of Schmidt-Hieber (2021). These are external, citable mathematical results, not self-citations, and the paper does not rely on them to fit the empirical numbers. The Kolmogorov–Arnold encoder Φ is explicitly tested and found empirically brittle (Table 11), so the main FAF results do not secretly depend on the lossless construction. Self-citations (Rubio-Madrigal et al. 2025, Mustafa & Burkholz 2024a/b, Jamadandi et al. 2024, Reddy et al. 2026a) appear in related-work context or as optional feature augmentations (Table 12), not as load-bearing support for the paper's central claim. The abstract's '12 tasks' count is internally inconsistent with Section 5's 'trail on 4' and Table 1, but that is a correctness/consistency problem, not a circularity of derivation: no equation reduces a predicted result to its own input. The paper also explicitly labels the two-hop behavior as information-losing and frames the low-hop sufficiency as an experimentally motivated hypothesis rather than as a derived consequence. Therefore no circular step can be exhibited with the required specificity, and the appropriate circularity score is 0.
Assumptions & free parameters
free parameters (4)
- FAF variant selection (reducer set) =
per-dataset: e.g., FAFmean on Computer, FAF4 on Pubmed
- MLP hyperparameters =
per-dataset dropout, lr, normalization, hidden channels, weight decay, MLP layers (Table 4)
- Hop depth K =
taken from best GNN depth per dataset, e.g., 2 for Computer, 15 for Minesweeper, restricted when OOM
- Weight decay range =
0, 1e-2, 1e-3, 5e-4, 5e-5
assumptions (4)
- domain assumption Sum aggregation is injective on multisets of orthogonal features of bounded size (Theorem 4.1).
- standard math Kolmogorov-Arnold representation variant (Theorem 2 of Schmidt-Hieber, 2021): existence of monotone φ and injective Φ on [0,1]^d (Theorem 4.2).
- standard math No continuous, permutation-invariant aggregation can be injective on all multisets of real vectors (Corso et al., 2020; Netto dimension obstruction).
- ad hoc to paper An MLP trained on concatenated fixed features generalizes comparably to GNNs under the same splits and tuning budget.
Cite this review
Pith. "Pith review of Fixed Aggregation Features Can Rival GNNs." pith.science (2026). https://pith.science/paper/X75KBF4J
@misc{pith2026260119449,
author = {Pith},
title = {Pith review of: Fixed Aggregation Features Can Rival GNNs},
year = {2026},
howpublished = {\url{https://pith.science/paper/X75KBF4J}},
note = {Machine review of arXiv:2601.19449}
}
read the original abstract
Graph neural networks (GNNs) are widely believed to excel at node representation learning through trainable neighborhood aggregations. We challenge this view by introducing Fixed Aggregation Features (FAFs), a training-free approach that transforms graph learning tasks into tabular problems. This simple shift enables the use of well-established tabular methods, offering strong interpretability and the flexibility to deploy diverse classifiers. Across 14 benchmarks, well-tuned multilayer perceptrons trained on FAFs rival or outperform state-of-the-art GNNs and graph transformers on 12 tasks -- often using only mean aggregation. The only exceptions are the Roman Empire and Minesweeper datasets, which typically require unusually deep GNNs. To explain the theoretical possibility of non-trainable aggregations, we connect our findings to Kolmogorov-Arnold representations and discuss when mean aggregation can be sufficient. In conclusion, our results call for (i) richer benchmarks benefiting from learning diverse neighborhood aggregations, (ii) strong tabular baselines as standard, and (iii) employing and advancing tabular models for graph data to gain new insights into related tasks.
Figures
Figures from the paper (6 more)
Reference graph
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