REVIEW 2 major objections 4 minor 46 references
Tensor-power sample spectra converge to the Marchenko–Pastur law even when the base vector's coordinates are dependent, provided the vector is exchangeable, sign-symmetric, and satisfies three moment conditions.
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
2026-08-01 06:45 UTC pith:BFOW5XBR
load-bearing objection The principal-tensor theorem is solid and genuinely new; the full tensor-power extension is delegated to a prior independent-coordinate proof and needs real work before the headline claim is earned. the 2 major comments →
Marchenko-Pastur law for tensor powers of exchangeable unconditional vectors
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The central claim is Theorem 2.1: for an exchangeable and unconditional base vector X in R^n — meaning the law is invariant under coordinate permutation and under independent sign flips — the sample covariance matrix of m i.i.d. copies of the principal tensor, whose coordinates are the products X_{i1}⋯X_{id} over all d-subsets, has ESD converging a.s. to the Marchenko–Pastur law μ_MP(c) when p/m→c and three moment conditions hold: (A) E(X₁²⋯X_d²)→1; (B) E(X₁²⋯X_{2d}²) converges to the square of the same block moment; and (C) the block fourth moments E(X₁⁴⋯X_r⁴ X_{r+1}²⋯X_{2d−r}²) are bounded by L^r with L d²/n→0. The paper derives easier sufficient conditions for fixed d and for diverging d,
What carries the argument
The carrying object is the symmetry hypothesis. Exchangeability lets the analysis track only moments in the first j coordinates, while the unconditional (sign-symmetric) property eliminates every mixed moment with an odd exponent. These reductions turn the concentration of an arbitrary quadratic form xᵀAx into sums over pairs of d-subsets with overlap r, controlled by combinatorial estimates (Leibniz-like bounds on binomial ratios) together with the block-moment conditions. For fixed d, an approximation of finite exchangeable laws by mixtures of product measures converts the moment conditions into elementary ones; for growing d, concentration of the ℓ₂ and ℓ₄ norms plays the same role.
Load-bearing premise
The base vector must be unconditional: independently flipping any subset of its coordinates must leave the distribution unchanged, because the proof uses this symmetry to discard every mixed moment containing an odd exponent.
What would settle it
The most direct falsifier is a counterexample sequence: an exchangeable, unconditional base vector X satisfying conditions (A)–(C) for which the ESD of the principal-tensor sample covariance matrix does not converge weakly to μ_MP(c). A concrete place to look is the boundary d=o(√n), where the combinatorial estimates in Section 5 start to degrade. Alternatively, fix d=1 and search for an exchangeable, unconditional X with E X₁²→1 and E X₁⁴≤L (so (A)–(C) hold) but for which the variance of the diagonal quadratic form xᵀAx with A=diag(1,0,...,0) does not tend to 0 after normalization by p²; Theo
If this is right
- For fixed tensor degree d, the result follows from E X₁²→1, the asymptotic uncorrelatedness of X₁² and X₂², and a uniform (4d+ε)-moment bound — conditions that are easy to check for many dependent models.
- For d→∞, the theorem holds whenever d=o(√n) and the normalized powers of the ℓ₂ and ℓ₄ norms concentrate; subexponential norm concentration gives d=o(n^{1/3}), and sub-Gaussian ℓ₄ concentration gives d=o(n^{1/2}).
- The same Marchenko–Pastur limit transfers to full tensor powers X^{⊗d}: after removing repetitions, the nontrivial eigenvalues, scaled by 1/d!, follow the same limiting spectrum.
- Multiplying each sample by an independent random radius produces a weighted Marchenko–Pastur law whose Stieltjes transform is determined by the radius distribution.
- Uniform measures on ℓ_k spheres and balls (including k<1), signed permutations, mixtures of i.i.d. symmetric laws, and isotropic log-concave measures with bounded Poincaré or log-Sobolev constants all satisfy the hypotheses.
- The paper explicitly notes that the exchangeable setting prevents an 'if and only if' result, because the population covariance is not generally the identity matrix; the criterion is sufficient, not necessary.
Where Pith is reading between the lines
- The sign-symmetry assumption is load-bearing: the proof discards all odd-exponent mixed moments at the point where the off-diagonal quadratic-form variance is bounded. A natural test is to see whether an exchangeable but non-sign-symmetric model (for example, a ferromagnetic spin vector) still yields the Marchenko–Pastur limit, or whether this is where the theorem genuinely fails.
- Because tensor-power sample covariance matrices have the same spectrum as power-function kernel matrices, the result implies that for these kernels the limiting spectrum depends only on low-order block moments of the data law, not on its full distribution — a step toward kernel universality for exchangeable unconditional data.
- A testable extension would be to weaken 'unconditional' to 'symmetric under a subgroup of sign changes' or to require only that odd mixed moments vanish asymptotically; the variance bounds in Section 5 suggest the proof would survive with only mild extra terms, but this is not established in the paper.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies the empirical spectral distribution (ESD) of sample covariance matrices built from i.i.d. copies of tensor powers of an exchangeable and unconditional random vector X in R^n. Theorem 2.1 provides sufficient conditions (A)-(C) on mixed moments of X under which the ESD for the principal tensor model PrincipalT(n,d,X) converges almost surely to the Marchenko-Pastur law, with p = C(n,d) and p/m -> c. The proof in Section 5 verifies the quadratic-form concentration condition of Yaskov via a detailed counting argument. The paper then gives easier-to-check conditions for fixed d (Theorem 2.2) and diverging d (Theorem 2.4), as well as extensions to weighted versions (Theorem 2.3) and to the full tensor power model PowerT(n,d,X) (Theorem 2.6), the latter through the reduced symmetric tensor model. Several examples are provided, including mixtures of product measures, uniform signed permutations, log-concave vectors, and ℓ_k-spherical distributions.
Significance. If the tensor-power extension (Theorem 2.6) is fully established, the paper significantly broadens the scope of Marchenko-Pastur laws beyond the independent-coordinate setting, covering structured dependent base vectors such as ℓ_k-spherical and log-concave ones. The principal-tensor theorem (Theorem 2.1) is proved in detail: the counting in Section 5 is careful, the use of exchangeability and unconditionality is explicit, and the conditions are stated in terms of checkable block moments. The paper also names and uses Yaskov's necessary-and-sufficient criterion, which helps pin down exactly what is needed. However, the headline claim for full tensor powers is not yet fully supported, as detailed below.
major comments (2)
- [Section 8, Eq. (29)] The proof of Theorem 2.6 hinges on the estimate (29), verbatim: 'The full argument for (29) is almost exactly the same as [43, Proposition 3.3]' and the only verification supplied is convergence of ||X||_2^{2d}/n^d to 1 in probability. This is not sufficient. The reduced tensor y ~ ReducedT(n,d,X) contains coordinates with repeated indices (e.g., sqrt(2) X_i^2 for d=2), so y^T B y includes self- and cross-terms involving these repeated monomials. Yaskov's Proposition 3.3 was proved for base vectors with independent coordinates; for exchangeable unconditional X, controlling those terms requires additional estimates (e.g., factorizations of E[X_i^2 X_j^2] that do not follow from conditions (A)-(C) or from the hypotheses of Theorems 2.2/2.4). The manuscript does not provide the missing argument, so the advertised extension to tensor powers rests on an unverified delegation.
- [Section 2.4 / Theorem 2.6 statement] The theorem states a limit for the ESD of eigenvalues divided by d!, but the proof sketch only discusses ESD(K_ReducedT). The equivalence between eigenvalues of K_PowerT and d! times eigenvalues of K_ReducedT is invoked from [43, Proposition 3.2] without proof or even a precise statement in the text. If this equivalence is not perfectly known for the present exchangeable setting (as opposed to the independent-coordinate setting), the proof should at least state the proposition and indicate why it continues to hold. As it stands, the chain from PowerT to ReducedT to PrincipalT is not completely transparent.
minor comments (4)
- [Section 5, Eq. (10)-(11)] The use of unconditionality to discard mixed moments with odd exponents is stated, but it would help to explicitly mention that the exchangeability is used to reduce to the first coordinates and that the odd-exponent condition is essential; otherwise a reader might miss why the proof does not work for, e.g., Curie-Weiss base vectors.
- [Section 8 title] The section heading 'Theorem 2.6 for the the tensor power model' contains a duplicated 'the'.
- [Section 2.4] The phrase 'with feature sizend' is likely meant to be 'size n^d' or 'feature space dimension n^d'; please clarify.
- [Remark after Theorem 2.1] In the remark for d=1, the text says conditions (A)(C) correspond to EX_1^2 -> 1 and EX_1^4 = o(p), but condition (C) is stated with L r and r up to d; for d=1 this reads EX_1^4 <= L, not o(p). Please align the remark with the actual condition (C) as stated.
Circularity Check
No significant circularity; the main theorem verifies an external sufficient condition directly, and the flagged tensor-power gap is an omitted proof, not a circular reduction.
full rationale
The derivation chain for the principal-tensor result (Theorem 2.1) is self-contained: it invokes Yaskov's external criterion (Theorem 4.1, from [44]/[41]) and then proves its hypothesis (5) by bounding Var(x^T A x) = o(p^2) directly from conditions (A)-(C). These moment conditions are stated independently and are not defined in terms of the MP law; no parameter is fitted to the target ESD. The proof uses the exchangeable/unconditional symmetries to discard odd mixed moments (Section 5, eqs. (10)-(11)), which narrows the scope of the theorem but is not a circular step. The tensor-power extension (Theorem 2.6, Section 8) does contain a load-bearing delegation: equation (29) is said to follow "almost exactly the same as [43, Proposition 3.3]" after only verifying norm concentration, without showing that the repeated-index cross terms of ReducedT satisfy the required variance bound. This is a genuine omitted-support issue, but it is not circularity: [43] is an external prior work, the delegation is to an independent benchmark, and the paper does not redefine its conclusion as an input. No self-citation chain, no by-construction equation identity, and no fitted-input-called-prediction pattern is present. Under the hard rules, a proof gap without a self-referential definitional reduction does not raise the circularity score.
Axiom & Free-Parameter Ledger
axioms (4)
- standard math Yaskov's criterion (Theorem 4.1): if (x^T A x - tr A)/p -> 0 in probability for all bounded PSD A, then ESD(K) => mu_MP(c).
- standard math Muirhead's inequality / Schur-convexity of mixed moments of exchangeable nonnegative variables (Lemma 4.3).
- standard math Diaconis-Freedman finite exchangeable sequence approximation (Theorem 4.4).
- standard math Klartag's logarithmic bound on the Poincare constant of isotropic log-concave measures.
read the original abstract
Given an isotropic, exchangeable, and unconditional random vector $\mathbf X$, we consider the sample covariance matrix constructed from i.i.d. copies of several tensor models of $\mathbf X$, such as the tensor power $\mathbf{X}^{\otimes d}$. Under appropriate moment conditions on $\mathbf X$, we show that almost surely, the empirical spectral distribution converges weakly to the Marchenko-Pastur law. This extends previous results which required the coordinates of $\mathbf X$ to be independent. As we demonstrate, our extension applies to many new random vectors $\mathbf X$ of interest.
Reference graph
Works this paper leans on
-
[1]
Some remarks on the Dozier-Silverstein theorem for random matrices with dependent entries
Radosław Adamczak. “Some remarks on the Dozier-Silverstein theorem for random matrices with dependent entries”.Random Matrices Theory Appl.2 (2013), pp. 1250017, 46
2013
-
[2]
Circular law for random matrices with exchangeable entries
Radosław Adamczak, Djalil Chafaï, and Paweł Wolff. “Circular law for random matrices with exchangeable entries”.Random Structures Algorithms3 (2016), pp. 454–479
2016
-
[3]
Random tensor theory: ex- tending random matrix theory to mixtures of random product states
Andris Ambainis, Aram W. Harrow, and Matthew B. Hastings. “Random tensor theory: ex- tending random matrix theory to mixtures of random product states”.Comm. Math. Phys.1 (2012), pp. 25–74
2012
-
[4]
Random points in the unit ball ofln p
Guillaume Aubrun. “Random points in the unit ball ofln p”.Positivity4 (2006), pp. 755–759
2006
-
[5]
Silverstein.Spectral analysis of large dimensional random matrices
Zhidong Bai and Jack W. Silverstein.Spectral analysis of large dimensional random matrices. Second. Springer, New York, 2010, pp. xvi+551
2010
-
[6]
Large sample covariance matrices without independence struc- tures in columns
Zhidong Bai and Wang Zhou. “Large sample covariance matrices without independence struc- tures in columns”.Statist. Sinica2 (2008), pp. 425–442. 32 REFERENCES
2008
-
[7]
On convex bodies and log-concave probability measures with unconditional basis
S. G. Bobkov and F. L. Nazarov. “On convex bodies and log-concave probability measures with unconditional basis”.Geometric aspects of functional analysis. Springer, Berlin, 2003, pp. 53–69
2003
-
[8]
Marchenko-Pastur law with relaxed independence conditions
Jennifer Bryson, Roman Vershynin, and Hongkai Zhao. “Marchenko-Pastur law with relaxed independence conditions”.Random Matrices Theory Appl.4 (2021), Paper No. 2150040, 28
2021
-
[9]
A generalization of the Lindeberg principle
Sourav Chatterjee. “A generalization of the Lindeberg principle”.Ann. Probab.6 (2006), pp. 2061–2076
2006
-
[10]
The spectrum of random inner-product kernel matrices
Xiuyuan Cheng and Amit Singer. “The spectrum of random inner-product kernel matrices”. Random Matrices Theory Appl.4 (2013), pp. 1350010, 47
2013
-
[11]
On spectral distribution of sample covari- ance matrices from large dimensional and largek-fold tensor products
Benoît Collins, Jianfeng Yao, and Wangjun Yuan. “On spectral distribution of sample covari- ance matrices from large dimensional and largek-fold tensor products”.Electron. J. Probab. (2022), Paper No. 102, 18
2022
-
[12]
Finiteexchangeablesequences
P.DiaconisandD.Freedman.“Finiteexchangeablesequences”.Ann. Probab.4(1980),pp.745– 764
1980
-
[13]
On empirical spectral distributions for random tensor product models
Simona Diaconu. “On empirical spectral distributions for random tensor product models”. arXiv preprint arXiv:2602.01242(2026)
arXiv 2026
-
[14]
The spectrum of random kernel matrices: universality results for rough and varying kernels
Yen Do and Van Vu. “The spectrum of random kernel matrices: universality results for rough and varying kernels”.Random Matrices Theory Appl.3 (2013), pp. 1350005, 29
2013
-
[15]
Sofiia Dubova, Yue M. Lu, Benjamin McKenna, and Horng-Tzer Yau. “Universality for the global spectrum of random inner-product kernel matrices in the polynomial regime”.arXiv preprint arXiv:2310.18280(2023)
Pith/arXiv arXiv 2023
-
[16]
Eaton.Multivariate statistics
Morris L. Eaton.Multivariate statistics. A vector space approach. John Wiley & Sons, Inc., New York, 1983, pp. xvi+512
1983
-
[17]
Chapman and Hall, Ltd., London, 1990, pp
Kai Tai Fang, Samuel Kotz, and Kai Wang Ng.Symmetric multivariate and related distribu- tions. Chapman and Hall, Ltd., London, 1990, pp. x+220
1990
-
[18]
High-dimensional sample covariance matrices with Curie-Weiss entries
Michael Fleermann and Johannes Heiny. “High-dimensional sample covariance matrices with Curie-Weiss entries”.ALEA Lat. Am. J. Probab. Math. Stat.2 (2020), pp. 857–876
2020
-
[19]
Between Paouris concentration inequality and variance conjecture
Bruno Fleury. “Between Paouris concentration inequality and variance conjecture”.Ann. Inst. Henri Poincaré Probab. Stat.2 (2010), pp. 299–312
2010
-
[20]
Gamelin.Complex analysis
Theodore W. Gamelin.Complex analysis. Springer-Verlag, New York, 2001, pp. xviii+478
2001
-
[21]
L p-norm spherical distribution
A. K. Gupta and D. Song. “L p-norm spherical distribution”.J. Statist. Plann. Inference2 (1997), pp. 241–260
1997
-
[22]
A class of statistics with asymptotically normal distribution
Wassily Hoeffding. “A class of statistics with asymptotically normal distribution”.Ann. Math. Statistics(1948), pp. 293–325
1948
-
[23]
Isoperimetric problems for convex bodies and a localization lemma
R. Kannan, L. Lovász, and M. Simonovits. “Isoperimetric problems for convex bodies and a localization lemma”.Discrete Comput. Geom.3-4 (1995), pp. 541–559
1995
-
[24]
Logarithmic bounds for isoperimetry and slices of convex sets
Bo’az Klartag. “Logarithmic bounds for isoperimetry and slices of convex sets”.Ars Inven. Anal.(2023), Paper No. 4, 17
2023
-
[25]
Affirmative resolution of Bourgain’s slicing problem using Guan’s bound
Bo’az Klartag and Joseph Lehec. “Affirmative resolution of Bourgain’s slicing problem using Guan’s bound”.Geom. Funct. Anal.4 (2025), pp. 1147–1168
2025
-
[26]
ModifiedPaourisinequality
RafałLatała.“ModifiedPaourisinequality”.Geometric aspects of functional analysis.Springer, Cham, 2014, pp. 293–307
2014
-
[27]
American Mathematical Society, Providence, RI, 2001, pp
Michel Ledoux.The concentration of measure phenomenon. American Mathematical Society, Providence, RI, 2001, pp. x+181
2001
-
[28]
An equivalence principle for the spectrum of random inner- product kernel matrices with polynomial scalings
Yue M. Lu and Horng-Tzer Yau. “An equivalence principle for the spectrum of random inner- product kernel matrices with polynomial scalings”.Ann. Appl. Probab.4 (2025), pp. 2411– 2470. REFERENCES 33
2025
-
[29]
Central limit theorem for linear eigenvalue statistics for a tensor product version of sample covariance matrices
A. Lytova. “Central limit theorem for linear eigenvalue statistics for a tensor product version of sample covariance matrices”.J. Theoret. Probab.2 (2018), pp. 1024–1057
2018
-
[30]
Distribution of eigenvalues in certain sets of random matrices
V. A. Marchenko and L. A. Pastur. “Distribution of eigenvalues in certain sets of random matrices”.Mat. Sb. (N.S.)(1967), pp. 507–536
1967
-
[31]
Marshall, Ingram Olkin, and Barry C
Albert W. Marshall, Ingram Olkin, and Barry C. Arnold.Inequalities: theory of majorization and its applications. Second. Springer, New York, 2011, pp. xxviii+909
2011
-
[32]
Theodor Misiakiewicz. “Spectrum of inner-product kernel matrices in the polynomial regime and multiple descent phenomenon in kernel ridge regression”.arXiv preprint arXiv:2204.10425 (2022)
Pith/arXiv arXiv 2022
-
[33]
On the limiting empirical measure of eigenvalues of the sum of rank one matrices with log-concave distribution
A. Pajor and L. Pastur. “On the limiting empirical measure of eigenvalues of the sum of rank one matrices with log-concave distribution”.Studia Math.1 (2009), pp. 11–29
2009
-
[34]
Universality of kernel random matrices and kernel regression in the quadratic regime
Parthe Pandit, Zhichao Wang, and Yizhe Zhu. “Universality of kernel random matrices and kernel regression in the quadratic regime”.J. Mach. Learn. Res.(2025), Paper No. [224], 73
2025
-
[35]
Approximate independence of distributions on spheres and their stability properties
S. T. Rachev and L. Rüschendorf. “Approximate independence of distributions on spheres and their stability properties”.Ann. Probab.3 (1991), pp. 1311–1337
1991
-
[36]
On the volume of the intersection of twoLn p balls
G. Schechtman and J. Zinn. “On the volume of the intersection of twoLn p balls”.Proc. Amer. Math. Soc.1 (1990), pp. 217–224
1990
-
[37]
Uniform distributions on spheres in finite-dimensionalL α and their generalizations
PawełJ. Szabłowski. “Uniform distributions on spheres in finite-dimensionalL α and their generalizations”.J. Multivariate Anal.2 (1998), pp. 103–117
1998
-
[38]
The asymptotic expansion of a ratio of gamma functions
F. G. Tricomi and A. Erdélyi. “The asymptotic expansion of a ratio of gamma functions”. Pacific J. Math.(1951), pp. 133–142
1951
-
[39]
Roman Vershynin.High-dimensional probability: an introduction with applications in data sci- ence. Second. Cambridge University Press, 2026
2026
-
[40]
Precise learning curves and higher-order scaling limits for dot-product kernel regression
Lechao Xiao, Hong Hu, Theodor Misiakiewicz, Yue M. Lu, and Jeffrey Pennington. “Precise learning curves and higher-order scaling limits for dot-product kernel regression”.J. Stat. Mech. Theory Exp.11 (2023), Paper No. 114005, 47
2023
-
[41]
Spectra of large dimensional random Gram matrices under partial dependence
P. A. Yaskov. “Spectra of large dimensional random Gram matrices under partial dependence”. Uspekhi Mat. Nauk5(485) (2025), pp. 105–174
2025
-
[42]
A remark on the spectrum of sample covariance matrices from large random tensors
Pavel Yaskov. “A remark on the spectrum of sample covariance matrices from large random tensors”.ALEA Lat. Am. J. Probab. Math. Stat.2 (2025), pp. 1301–1307
2025
-
[43]
Marchenko–Pasturlawforarandomtensormodel
PavelYaskov.“Marchenko–Pasturlawforarandomtensormodel”.Electron. Commun. Probab. (2023), Paper No. 23, 17
2023
-
[44]
Necessary and sufficient conditions for the Marchenko–Pastur theorem
Pavel Yaskov. “Necessary and sufficient conditions for the Marchenko–Pastur theorem”.Elec- tron. Commun. Probab.(2016), Paper No. 73, 8
2016
-
[45]
Limit theorem for the eigenvalues of the sample covariance matrix when the underlying distribution is isotropic
Y. Q. Yin and P. R. Krishnaiah. “Limit theorem for the eigenvalues of the sample covariance matrix when the underlying distribution is isotropic”.Teor. Veroyatnost. i Primenen.4 (1985), pp. 810–816
1985
-
[46]
On spectrum of sample covariance matrices from large tensor vectors
Wangjun Yuan. “On spectrum of sample covariance matrices from large tensor vectors”.ALEA Lat. Am. J. Probab. Math. Stat.2 (2024), pp. 1527–1545. Department of Mathematics, University of W ashington, Seattle, W A 98195, USA Email address:fecheng@uw.edu Department of Mathematics, University of W ashington, Seattle, W A 98195, USA Email address:danmiku@uw.edu
2024
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.