REVIEW 2 major objections 3 minor 34 references
On Euclidean Hulls of MDS Codes
T0 review · 2 major / 3 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read From any self-orthogonal generalized Reed-Solomon code, this paper builds maximum distance separable codes with every prescribed Euclidean hull dimension.
desk verdict Theorems 1 and 2 are correct and genuinely general, but Corollary 3.2(ii) has a proof gap: the extended GRS code of a self-dual GRS seed is not self-orthogonal in general, so the stated derivation from Theorem 2 does not work. 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 load-bearing object is the multiplier vector $\mathbf{v}$ of a GRS code together with the numbers $u_i = \prod_{j \neq i}(a_i - a_j)^{-1}$. Lemma 2.4 characterizes self-orthogonality: $\mathrm{GRS}_m(\mathbf{a},\mathbf{v})$ is Euclidean self-orthogonal if and only if $v_i^2 = \lambda(a_i)u_i$ for every $i$, with $\lambda$ a polynomial of degree at most $n-2m$; Lemma 2.5 gives the extended analogue with $\lambda(x) = \lambda_0 + \cdots + \lambda_{n-2m}x^{n-2m} - x^{n-2m+1}$. Given such a code, the construction scales the first $s$ entries of $\mathbf{v}$ by $\alpha$ with $\alpha^2 \neq 1$. Comparing the first $s$ positions with the remaining $n-s$ positions in the hull equations (Lemmas 2.1 and 2.2) yields $(\alpha^2 - 1)\lambda(a_i)u_i f(a_i) = 0$, so $f(a_i) = 0$ for $i \leq s$. Conversely every polynomial divisible by $\prod_{i=1}^s (x-a_i)$ gives a hull codeword, so the hull has exactly dimension $k-s$.
What would settle it
Over $\mathbb{F}_9$, take a self-orthogonal $\mathrm{GRS}_2(\mathbf{a},\mathbf{v})$ satisfying the condition of Lemma 2.4, set $s=1$, pick $\alpha$ with $\alpha^2 \neq 1$, and form $\mathbf{v}'$ by scaling the first coordinate; computing the hull dimensions of $\mathrm{GRS}_1(\mathbf{a},\mathbf{v}')$ and $\mathrm{GRS}_2(\mathbf{a},\mathbf{v}')$ should give $0$ and $1$ respectively. Alternatively, one can check a square-residue claim in Example 4.1 directly: for the constructed set $A$, test whether $\prod_{z \neq i}(a_i - a_z)$ is a square in $\mathbb{F}_q$ for every $i$.
Extended reading notes
Core claim
The central claim is Theorem 1: assume $1 \leq m \leq \lfloor n/2 \rfloor$ and $q > 3$, and suppose the GRS code $\mathrm{GRS}_m(\mathbf{a},\mathbf{v})$ is Euclidean self-orthogonal (contained in its Euclidean dual). Then for every $0 \leq l \leq k \leq m$ there exists a $q$-ary $[n,k]$ MDS code $C$ with $\dim \mathrm{Hull}(C) = l$. Theorem 2 gives the extended-GRS version: under $n < q$, a self-orthogonal extended GRS code of dimension $m$ yields $[n+1,k]$ MDS codes with any hull dimension $l \leq k \leq m$. The construction is explicit: set $s = k-l$, pick $\alpha \in \mathbb{F}_q^*$ with $\alpha^2 \neq 1$, and form $\mathbf{v}'$ by multiplying the first $s$ coordinates of $\mathbf{v}$ by $\alpha$ (for extended codes, also by the factor $(x-b)^{m-k}$ evaluated at each $a_i$ with $b \notin \{a_1,\dots,a_n\}$). The hull of $C = \mathrm{GRS}_k(\mathbf{a},\mathbf{v}')$ consists exactly of codewords whose defining polynomial $f$ has $a_1,\dots,a_s$ as roots, so its dimension is $k-s = l$.
Load-bearing premise
The construction assumes that a self-orthogonal (extended) GRS code of dimension $m$ with the multiplier form $v_i^2 = \lambda(a_i)u_i$ actually exists; the infinite families in the examples depend on square-residue claims from the authors' earlier paper that are not proved here.
Editorial extensions
If this is right
- Every known self-orthogonal or self-dual (extended) GRS code automatically yields MDS codes with all hull dimensions from $0$ up to $k$, removing the need for separate constructions for each hull size.
- The resulting codes with hull dimension $l$ translate into entanglement-assisted quantum error-correcting codes whose number of required entangled states is tied to $l$, so the construction makes EAQECC parameters flexible.
- Corollaries 3.1 and 3.2 recover earlier MDS hull constructions as special cases, so the mechanism subsumes previously known results.
- Example 4.4 supplies a family where no self-dual MDS code can exist ($q \equiv 3 \pmod{4}$, $n \equiv 2 \pmod{4}$), showing the self-orthogonal assumption reaches cases the self-dual route cannot.
Reading between the lines
- The scaling trick seems to be independent of the GRS structure beyond the hull equation, so a similar 'rescale the generator to pin the hull' mechanism may apply to any code whose hull can be characterized by polynomial vanishing; the paper leaves this open.
- The same argument with $\alpha^2 \neq 1$ replaced by a $q$-th power condition could plausibly construct Hermitian hulls of prescribed dimensions, an extension the paper does not make.
- The $q=3$ examples in Remark 3.3 suggest the condition $q > 3$ is not an artifact of the proof but a genuine threshold, since a 3-ary $[4,2]$ code cannot have hull dimension $1$.
- One direct check: for a small field, pick any self-orthogonal $\mathrm{GRS}_2$ code, choose $\alpha = 2$ say, and compute the hull of $\mathrm{GRS}_1$ and $\mathrm{GRS}_2$ with the scaled multiplier; the dimensions should match the theorem exactly.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes a general mechanism for constructing q-ary MDS codes with a prescribed dimension l of the Euclidean hull. The input is a self-orthogonal GRS code GRS_m(a,v) (Theorem 1) or extended GRS code GRS_m(a,v,∞) (Theorem 2) of dimension m; from it the authors construct, for any 0 ≤ l ≤ k ≤ m, an [n,k] (or [n+1,k]) MDS code with hull dimension exactly l. The construction multiplies an initial segment of the entries of v by a scalar α with α^2≠1 and, in the extended case, factors in a polynomial π(x) of degree m-k. A hull-vector argument shows that the hull consists precisely of those codewords whose associated polynomial vanishes at the first s=k-l coordinates. Several corollaries and concrete families (q=r^2, q=p^{2s}, q≡3 mod 4) are derived from known self-dual and almost self-dual GRS seeds.
Significance. The proposed mechanism is clean and, conditional on the existence of suitable self-orthogonal seeds, delivers MDS codes with arbitrary hull dimensions, subsuming several earlier constructions (Remarks 3.1 and 3.2). The proofs of Theorems 1 and 2 are complete: the degree bounds in Lemmas 2.4 and 2.5 are correct, and the polynomial-identity arguments that identify the hull are rigorous. The paper makes the role of the seed codes transparent and frames a natural open problem. However, the proof of Corollary 3.2(ii) has a gap, and the examples depend on the authors' preprint [12] for seed existence, so the paper as submitted is not yet ready for acceptance.
major comments (2)
- [Section 3, Corollary 3.2(ii) and Section 4, Example 4.1(ii)] The claimed direct derivation of Corollary 3.2(ii) from Theorem 2 is invalid. Self-duality of GRS_{n/2}(a,v) gives v_i^2 = λ_0 u_i with λ_0 constant by Corollary 2.1, whereas Theorem 2 requires the extended code GRS_{n/2}(a,v,∞) to be self-orthogonal; by Lemma 2.5 that would require v_i^2 = (λ_0 - a_i)u_i, a condition not implied by the seed. The same gap appears in the proof of Example 4.1(ii), which invokes Theorem 2 after the same self-dual GRS seed. The corollary may be salvageable by a separate polynomial-identity argument, but the paper does not provide it.
- [Section 4, Examples 4.1–4.3] The constructions of the self-dual or almost self-dual seeds rely on square-residue statements taken from the authors' preprint [12] (e.g., 'by [12]' in the proofs of Examples 4.1 and 4.2). None of these statements is reproduced or proved in the present manuscript. If [12] is not available to the reader, the examples are not verifiable. The authors should include a proof or a precise statement of the needed lemmas, or explicitly label the examples as conditional on [12].
minor comments (3)
- [Abstract] The abstract contains typographical artifacts: 'MD S codes' and 'g eneralized' should be 'MDS codes' and 'generalized'.
- [Remark 3.3(iii)] The assertion that no 3-ary [4,2,3] code with hull dimension 1 exists is not accompanied by a calculation or a reference; please provide the verification.
- [Section 2, proof of Lemma 2.4] The phrase 'linear independent' should be 'linearly independent'.
Circularity Check
No circularity: the main theorems prove hull dimensions from a stated self-orthogonality assumption, and the cited self-dual seed results are external instantiations, not fitted inputs.
full rationale
The derivation chain is self-contained and conditional. Theorem 1 assumes GRS_m(a,v) is self-orthogonal and, via Lemma 2.4, represents v_i^2 = lambda(a_i)u_i; it then constructs C = GRS_k(a,v') by scaling s = k-l coordinates and proves from Lemma 2.1 that the hull consists exactly of functions vanishing at those s points, giving dim Hull(C)=l. No parameter is fitted to a subset of the hull data, and no quantity is renamed as a prediction: the hull dimension is computed, not assumed. Theorem 2 uses the analogous Lemma 2.5 and the same degree argument with pi(x)=(x-b)^{m-k}; again the output is derived from, not identified with, the self-orthogonality condition. The examples import square-residue seed codes from the authors' earlier preprint [12]; this is a self-citation, but it is not circular because [12] supplies the independent existence of a self-orthogonal/self-dual seed satisfying stated field-theoretic conditions, and the theorem only needs such a seed as a hypothesis. The questionable direct derivation in Corollary 3.2(ii) -- where an even-length self-dual GRS seed is used as if it made the extended GRS code self-orthogonal -- is a proof gap, not a circular reduction; the hull-dimension mechanism itself does not presuppose the conclusion.
Assumptions & free parameters
assumptions (5)
- standard math GRS_k(a,v) and its extended version are MDS and their duals are GRS codes (MacWilliams and Sloane, Chapter 11).
- domain assumption Lemma 2.1 and 2.2 from Chen and Liu [4] characterize the hull of GRS and extended GRS codes via polynomial identities.
- standard math Lemma 2.3 from Li, Xing, and Wang [21]: the power sums Σ a_i^m u_i vanish for m ≤ n-2 and equal 1 for m = n-1.
- domain assumption For the examples, the existence of self-dual or almost self-dual GRS codes with the required square-residue properties is taken from the authors' preprint [12].
- standard math The field size q satisfies q > 3, so there exists an element α with α^2 ≠ 1.
Cite this review
Pith. "Pith review of On Euclidean Hulls of MDS Codes." pith.science (2026). https://pith.science/paper/T7RNWVMM
@misc{pith2026190801173,
author = {Pith},
title = {Pith review of: On Euclidean Hulls of MDS Codes},
year = {2026},
howpublished = {\url{https://pith.science/paper/T7RNWVMM}},
note = {Machine review of arXiv:1908.01173}
}
read the original abstract
In this paper, we propose a mechanism on the constructions of MDS codes with arbitrary dimensions of Euclidean hulls. Precisely, we construct (extended) generalized Reed-Solomon(GRS) codes with assigned dimensions of Euclidean hulls from self-orthogonal GRS codes. It turns out that our constructions are more general than previous works on Euclidean hulls of (extended) GRS codes.
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Reviewed August 14, 2026 · model on record in the stance chip above.
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