alphaFeedback

WorksMathematics

Autocorrelation Phase Lattices on Cyclic Groups: Unit Supports, 2pq Orbit Profiles, and Binary Reconstruction

AI contributions
  • OpenAI Codex GPT-5.6 Sol
View details
Ancillary data
1 code link
View

Abstract

For a finite cyclic group and an exact Fourier support SS, we study the lattice L≤d(S)\mathcal{L}_{\le d}(S) generated by zero-sum relations of length at most dd inside the full relation lattice K(S)K(S). Its closing degree is both a local separating degree and the order at which every invisible phase ratio becomes a translation character. For the exact unit support of every even cyclic group, we compute ZUn/L≤4(Un)≅{Z/nZ,3∤n,Z⊕Z/(n/6)Z,6∣n. \mathbb{Z}^{U_{n}}/\mathcal{L}_{\le4}(U_{n})\cong \begin{cases} \mathbb{Z}/n\mathbb{Z},&3\nmid n,\\ \mathbb{Z}\oplus\mathbb{Z}/(n/6)\mathbb{Z},&6\mid n. \end{cases} Moreover L≤5(Un)=L≤4(Un)\mathcal{L}_{\le5}(U_{n})=\mathcal{L}_{\le4}(U_{n}). Thus fourth- and fifth-order rational ambiguity coincide: fourth order reconstructs up to translation when 3∤n3\nmid n, while for n=6mn=6m the complete surviving family has normalized ratios parameterized by norm-one elements of Q(ζ6)\mathbb{Q}(\zeta_6), modulo the residual translation subgroup μ6\mu_6; order six closes it. For n=2pqn=2pq with distinct odd primes, we classify every nonempty Aut⁡(Cn)\operatorname{Aut}(C_n)-stable support. The distributions of these 255 supports by closing degree are (1,2,154,80,4,14)(p=3),(1,2,154,92,4,2)(p,q≥5). (1,2,154,80,4,14)\quad(p=3),\qquad (1,2,154,92,4,2)\quad(p,q\ge5). The proof uses seven local CRT presentations, cubic and quartic Skeletons, and explicit depth-five and depth-six obstructions. Galois-equivariant lower-bound ratios show that the lattice, rational-signal and integer-signal closing degrees coincide on every stable support. Finally, for binary indicators, a supportwise crosswalk and a uniform exclusion of all deep supports give rset(C2pq)=4r_{\rm set}(C_{2pq})=4 under translations. The value is also four for the same oriented analytical deck when outputs are identified up to translation or reflected translation.

Copyright © 2026 Oleksiy Babanskyy. The repository’s MIT license applies to the assurance software, not to this manuscript. This Hexagon version is distributed under the Creative Commons Attribution 4.0 International license (CC BY 4.0).

Introduction and exact results

Higher-order autocorrelations are translation invariants built from products of a function along several shifted copies. Their use in pattern recognition and periodic reconstruction has a long history [2, 16, 4, 12]. On a finite cyclic group, the Fourier transform converts an order-kk autocorrelation into products over zero-sum kk-tuples. This makes reconstruction below the classical global order-six line of Grünbaum–Moore [8] a problem about the integral generation of zero-sum relations.

The answer depends sharply on the exact Fourier support. For a support S⊂CnS \subset C_n, let L≤d(S)\mathcal{L}_{\le d}(S) be generated by the nonnegative zero-sum multiplicity vectors of length at most dd, and let K(S)K(S) be the full integral relation lattice. We call

δ(S)=min⁡{d:L≤d(S)=K(S)}\delta(S) = \min\{d : \mathcal{L}_{\le d}(S) = K(S)\}

the local closing degree. Section 2 identifies it with the maximum separating-atom length on SS, using the established quotient-group language of Schefler–Zhao–Zhong [SZZ26]. Section 3 explains why the same lattice controls phase ratios invisible to autocorrelations.

We compute this object in two directions. The first is a signal-level theorem and complete ambiguity parametrization for the exact unit support of every even cyclic group. The second is a complete supportwise classification when the group order is 2pq2pq, together with exact rational and integer thresholds and explicit lower-bound pairs on every stable support of depth greater than one. The sole depth-one support is direct. Their common row is the unit orbit.

The orbit-stable classification

Let p<qp < q be distinct odd primes. The automorphism orbits in C2pqC_{2pq} are the eight element-order classes Od\mathcal{O}_d for d∣2pqd \mid2pq. Hence a rational Fourier support, which is stable under the Galois action, is a union of these eight orbits and there are 28−1=2552^8 - 1 = 255 nonempty possibilities.

Theorem 1.1 (Orbit-stable profiles). For n=2pqn = 2pq, the numbers of nonempty Aut⁡(Cn)\operatorname{Aut}(C_n)-stable supports of local closing degree 1,…,61,\ldots,6 are

(1,2,154,80,4,14)if p=3,(1, 2, 154, 80, 4, 14) \qquad\text{if } p = 3,

and

(1,2,154,92,4,2)if p,q≥5.(1, 2, 154, 92, 4, 2) \qquad\text{if } p,q \ge5.

Equivalently, these are the distributions of the maximum separating-atom length on the stable supports. In both regimes the orbit-stable local maximum is six.

For A∈{Q,Z}A \in\{\mathbb{Q},\mathbb{Z}\}, let δA(S)\delta_A(S) be the least d≥1d \ge1 such that any two AA-valued signals with exact Fourier support SS and equal autocorrelations of orders 1,…,d1,\ldots,d differ by a translation. The phase-ratio bridge gives the upper bounds δZ(S)≤δQ(S)≤δ(S)\delta_{\mathbb{Z}}(S) \le\delta_{\mathbb{Q}}(S) \le\delta(S). The reverse bounds require arithmetic realizations of the lattice obstructions and are the content of the following theorem.

Theorem 1.2 (Uniform rational and integer realization). Let n=2pqn = 2pq, where p<qp < q are distinct odd primes. For every nonempty Aut⁡(Cn)\operatorname{Aut}(C_n)-stable exact Fourier support SS,

δZ(S)=δQ(S)=δ(S).(1)\delta_{\mathbb{Z}}(S) = \delta_{\mathbb{Q}}(S) = \delta(S). \tag*{(1)}

Thus the rational-signal and integer-signal reconstruction profiles are the two profiles in Theorem 1.1. Equivalence is by translation only.

For a subset A⊂CnA \subset C_n, its analytical ordered kk-deck is (12) with f=1Af=1_A. Let rset(Cn)r_{\mathrm{set}}(C_n) be the least dd for which this dd-deck determines every subset up to translation. Indicators are idempotent, so zero shifts make the exact dd-deck contain every lower deck; this fact is special to the binary class. Lemma 11.1 shows, including for the empty set and sets of size below dd, that this is exactly Pebody’s cumulative necklace-deck convention rather than a different analytical reconstruction problem.

Theorem 1.3 (Binary reconstruction in the 2pq2pq family). If p<qp<q are distinct odd primes, then

rset(C2pq)=4.(2)r_{\mathrm{set}}(C_{2pq})=4. \tag*{(2)}

The upper bound follows by combining the supportwise phase-lattice criterion with a binary exclusion of every depth-five and depth-six support. The lower bound is the published even-order three-deck obstruction of Keleti–Kolountzakis [13].

Pebody determined the multiset reconstruction numbers of finite abelian groups and obtained the general cyclic set bound six [17 Theorems 2.1–2.2 and Lemma 9.3]. Combining his comparison of set and multiset reconstruction with the multiset classification and the even-order lower bound of Keleti–Kolountzakis already gives

rset(C2a)=4(a≥4),rset(C2ℓk)=4(ℓ>3 prime, 2ℓk>10).(3)r_{\mathrm{set}}(C_{2^a})=4 \quad(a\geq4), \qquad r_{\mathrm{set}}(C_{2\ell^k})=4 \quad(\ell>3\ \text{prime},\ 2\ell^k>10). \tag*{(3)}

Pebody later conjectured value four for every even cyclic order greater than ten and reported that his method covered many even orders, including every one below 240 [18]. Theorem 1.3 adds the arithmetically disjoint squarefree family 2pq2pq, with two distinct odd prime factors, inside that conjectural line; no absolute priority or firstness assertion is made.

The proof is uniform in the primes. It does not arise from interpolation of finite atlases. We first compute the cumulative degree-two, degree-three and degree-four presentations of seven nonzero CRT boxes. Exactly nineteen cubic box-count patterns can occur. Five propagation lemmas convert them into a ten-clause criterion selecting exactly 77 of the 127 nonempty seven-box masks; ten explicit defect families prove the converse. At order four, fourteen connector types reduce the generic branch to complete primary-coordinate graphs and the p=3p=3 branch to a fixed six-coordinate integral presentation. The remaining masks are two depth-five bridges and one or seven depth-six critical bases. Adding the optional zero orbit doubles every base row and gives the two displayed profiles.

The ordinary separating Noether number is a different invariant: it maximizes over modules and supports, and its exact finite-abelian value belongs to the separating-invariant literature [10]. Theorem 1.1 is a supportwise distribution restricted to the eight order orbits of one cyclic group.

There is also a closer general framework. Domokos characterizes separating monomials by integral generation of zero-sum sequence monoids, first for diagonalizable actions and then, over non-closed fields, by imposing the criterion on every Galois-stable character subset [6, 7]. That criterion explains why the stable supports considered here are the natural local objects. It does not give the least truncation degree for any prescribed support, the ten-clause Cubic Skeleton, either arithmetic profile, or the exact unit-support quotient. Theorem 1.1 computes precisely this supportwise layer for the regular representation of C2pqC_{2pq}.

Exact unit supports

Write Un=(Z/nZ)×U_n=(\mathbb{Z}/n\mathbb{Z})^\times. The second theorem begins with an integral dichotomy and then performs the Galois descent needed for rational signals.

Theorem 1.4 (Even unit-support dichotomy and signal classification). Let nn be even.

  1. The fourth-order quotient is

ZUn/L≤4(Un)≅{Cn,3∤n,Z⊕Cn/6,6∣n.(4)\mathbb{Z}^{U_n}/\mathcal{L}_{\leq4}(U_n)\cong \begin{cases} C_n, & 3\nmid n,\\ \mathbb{Z}\oplus C_{n/6}, & 6\mid n. \end{cases} \tag*{(4)}

If 6∣n6\mid n, then L≤6(Un)=K(Un)\mathcal{L}_{\leq6}(U_n)=K(U_n). In every even modulus, L≤5(Un)=L≤4(Un)\mathcal{L}_{\leq5}(U_n)=\mathcal{L}_{\leq4}(U_n).

  1. If 3∤n3\nmid n, every two rational-valued signals with exact Fourier support UnU_n and equal autocorrelations through order four differ by a translation.

  1. If n=6mn=6m, every pair with exact support UnU_n and equal data through order four has, after translating the second signal, the form

f^(u)=σu(α),g^(u)=σu(zα),(5)\widehat{f}(u)=\sigma_u(\alpha),\qquad\widehat{g}(u)=\sigma_u(z\alpha), \tag*{(5)}

where α∈Q(ζn)×\alpha\in\mathbb{Q}(\zeta_n)^\times and z∈Q(ζ6)×z\in\mathbb{Q}(\zeta_6)^\times satisfies zz‾=1z\overline{z}=1. Conversely every pair in (1.2) agrees through order five, and hence through order four. Normalized parameters are translation-equivalent exactly modulo μ6\mu_6, and equality at order six is equivalent to z6=1z^6=1.

The integral calculation uses a universal ambient group for the sifted set

Tq,c={t∈Cq:gcd⁡(1+ct,q)=1}.T_{q,c}=\{t\in C_q:\gcd(1+ct,q)=1\}.

It is a concrete use of the Freiman-homomorphism framework of Konyagin–Lev and Grynkiewicz [14, 9]. The exceptional free direction is not an arbitrary cyclotomic effect: it is the second admissible class modulo three. After translation and rational descent, the relative phase lies in the quadratic subfield even though the common amplitude ranges over the full cyclotomic field.

Corollary 1.5 (The common unit row). For n=2pqn=2pq, the unit support is the single orbit U2pq=O2pqU_{2pq}=O_{2pq}. Its closing degree is

δ(U2pq)={6,p=3,4,p,q≥5.\delta(U_{2pq})= \begin{cases} 6, & p=3,\\ 4, & p,q\geq5. \end{cases}

Theorem 1.1 and Theorem 1.4 therefore agree on their literal common support.

Corollary 1.6 (U30U_{30}). For exact support U30U_{30}, formula (1.2) is the complete rational classification through both orders four and five. The larger field Q(ζ30)\mathbb{Q}(\zeta_{30}) enlarges the common amplitude α\alpha, while the relative phase remains in the norm-one torus of Q(ζ6)\mathbb{Q}(\zeta_6).

This specializes to the question raised by Agulnick–Busick-Warner [1]; § 5 gives the precise comparison. The Fourier monomial and Galois criteria used in passing from lattices to signals are due to Casper–Orozco [3].

Claim levels and organization

The distinction between the two headline conclusions is binding. On the unit support, all surviving lattice characters are classified and rationally realized. On all 255 supports, we determine the exact rational and integer thresholds; whenever the depth exceeds one, we construct at least one Galois-equivariant lower-bound ratio for the failure immediately below closure. The sole depth-one support is handled directly. We do not classify the complete rational ambiguity torus on every atlas row.

Sections 2–5 establish the common dictionary and the unit-support theorem. Sections 6–9 prove the 2pq2pq lattice classification. Section 10 constructs the nontrivial supportwise rational and integer lower-bound pairs and proves Theorem 1.2. Section 11 specializes the classifier to binary indicators, proves Theorem 1.3, and records the oriented-deck translation/reflection corollary. Section 12 returns to autocorrelation and literature boundaries. The appendices record the full connector and Boolean tables and separate computational assurance from proof.

Scope boundary. No absolute priority or firstness assertion is made. The binary phase/deck crosswalk is part of the Pebody–Grünbaum–Moore–Simon lineage, and the even three-deck lower bound is imported from Keleti–Kolountzakis. The generic critical support used later is the sharpness family of Casper–Orozco; the global sixth-order line and the ratio-character method have earlier sources. The general non-closed-field separating criterion is Domokos’s. The contribution certified here is the displayed fixed-support theorem chain, its exact supportwise classification, and the explicit Galois-equivariant realization of every nontrivial lower-bound layer.

Zero-sum lattices and local separating degree

Let GG be a finite abelian group and let ∅≠S⊂G\varnothing\ne S \subset G. Write

B(S)={a∈N0S:∑s∈Sass=0}\mathcal{B}(S)=\left\{\boldsymbol{a}\in\mathbb{N}_0^S:\sum_{s\in S}a_s s=0\right\}

for the zero-sum sequence monoid. Its atoms are denoted by A(S)\mathcal{A}(S). For d≥1d\ge1, let B(S)≤d\mathcal{B}(S)_{\le d} be the submonoid generated by atoms of length at most dd. The integral relation lattice is

K(S)=ker⁡(ZS⟶⟨S⟩),(as)⟼∑sass,K(S)=\ker\left(\mathbb{Z}^S\longrightarrow\langle S\rangle\right),\qquad(a_s)\longmapsto\sum_s a_s s,

and L≤d(S)L_{\le d}(S) is generated by all nonnegative zero-sum vectors of length at most dd.

Using all rows of length at most dd or only atoms of length at most dd is equivalent at the integral level. A reducible zero-sum sequence factors as a sum of shorter zero-sum sequences and adds no new generator beyond its atoms. We retain the row language in coordinate proofs because one autocorrelation monomial naturally gives one row; the atom language is the bridge to separating invariants.

For reference, the objects used throughout are separated in Table 1. In particular, Ad(S)A_d(S) contains the finite target coordinates as well as the obstruction; it should not be called the ambiguity group.

ObjectDefinitionRole
B(S)\mathcal{B}(S)Nonnegative zero-sum sequencesMonoid of Fourier monomial indices
K(S)K(S)Full integral kernel in ZS\mathbb{Z}^{S}All additive relations on the support
L≤d(S)\mathcal{L}_{\le d}(S)Span of zero-sum rows through length ddRelations visible to bounded autocorrelations
Ad(S)A_d(S)ZS/L≤d(S)\mathbb{Z}^{S}/\mathcal{L}_{\le d}(S)Universal ambient presentation
K(S)/L≤d(S)K(S)/\mathcal{L}_{\le d}(S)Kernel of Ad(S)→⟨S⟩A_d(S) \to\langle S\rangleIntegral obstruction lattice
Hom⁡(K/L≤d,C×)\operatorname{Hom}(K/\mathcal{L}_{\le d},\mathbb{C}^{\times})Character dual of the obstructionComplex phase ambiguity modulo translations
δ(S)\delta(S)Least dd with L≤d=K\mathcal{L}_{\le d}=KLocal closing/separating degree

Table 1. Notation and logical roles.

For a cancellative monoid MM, write q(M)\mathrm{q}(M) for its quotient group. The next proposition is the precise bridge between the lattice used here and the separating-atom filtration of Schefler–Zhao–Zhong [SZZ26].

Proposition 2.1 (Group-completion dictionary). For every SS and dd,

L≤d(S)=q(B(S)≤d),K(S)=q(B(S)),(6)\mathcal{L}_{\le d}(S)=q(\mathcal{B}(S)_{\le d}), \qquad K(S)=q(\mathcal{B}(S)), \tag*{(6)}

where both quotient groups are viewed in ZS\mathbb{Z}^{S}. Consequently

δ(S)=max⁡{∣A∣:A∈Asep(S)},(7)\delta(S)=\max\{|A|:A\in\mathcal{A}_{\mathrm{sep}}(S)\}, \tag*{(7)}

the maximum length of a separating atom over SS.

Proof. Every nonnegative zero-sum vector of length at most dd factors into atoms, each of length at most dd. Conversely, each atom of length at most dd is one of the rows generating L≤d(S)\mathcal{L}_{\le d}(S). Taking integral differences gives the first identity in (6).

The inclusion q(B(S))⊂K(S)q(\mathcal{B}(S))\subset K(S) is immediate. For the reverse inclusion, let x=x+−x−∈K(S)x=x^{+}-x^{-}\in K(S). The two nonnegative parts have the same group sum, say h∈⟨S⟩h\in\langle S\rangle. Since the finite group ⟨S⟩\langle S\rangle is generated by SS, there is a nonnegative vector c∈N0Sc\in\mathbb{N}_{0}^{S} with group sum −h-h: begin with an integral expression and add suitable multiples of element orders to make every coefficient nonnegative. Then x++cx^{+}+c and x−+cx^{-}+c lie in B(S)\mathcal{B}(S) and their difference is xx.

By Definition 2.5 of [SZZ26], a separating atom is an atom not contained in the quotient group generated by shorter atoms. The same source proves that separating atoms generate the full quotient group. Thus the least truncation degree generating K(S)K(S) is their maximum length, which is (7).

The proposition does not require S=−SS=-S. This is useful because it separates the algebraic dictionary from Fourier rationality. When SS is the exact support of a rational-valued signal, Galois stability later implies S=−SS=-S, but no symmetry hypothesis is needed in Proposition 2.1.

Domokos’s lattice criterion for diagonalizable actions states the same generation principle at the level of coordinate subrepresentations [6 Theorem 1.3]. Its non-closed-field extension requires the criterion on every Galois-stable character subset of the regular representation [7 Theorem 5.4]. We use that result as the general field-theoretic boundary, not as a source of the numerical profiles: our local invariant asks for the least dd generating the group completion on each prescribed stable support. Sections 6–9 compute that truncation exactly for all 255 supports of C22pqC_{2}^{2p}q.

References

  1. [1]Aaron Agulnick and Toby Busick-Warner. Higher-order autocorrelations on finite abelian groups, 2026. arXiv:2604.13310v1.arxiv.org/abs/2604.13310
  2. [2]Roy L. Adler and Alan G. Konheim. A note on translation invariants. Proceedings of the American Mathematical Society, 13(3):425–428, 1962. DOI: 10.1090/S0002-9939-1962-0146652-1.DOI
  3. [3]W. Riley Casper and Bobby Orozco. Reconstructing rational functions on finite abelian groups with higher autocorrelations, 2026. arXiv:2503.21022v2.arxiv.org/abs/2503.21022
  4. [4]D. Chazan and B. Weiss. Higher order autocorrelation functions as translation invariants. Information and Control, 16(4):378–383, 1970.
  5. [5]Mátyás Domokos. Degree bound for separating invariants of abelian groups. Proceedings of the American Mathematical Society, 145(9):3695–3708, 2017.arxiv.org/abs/1602.06597
  6. [6]Mátyás Domokos. Separating monomials for diagonalizable actions. Bulletin of the London Mathematical Society, 55(1):205–223, 2023. arXiv:2202.07002v3; DOI: 10.1112/blms.12722.DOI
  7. [7]Mátyás Domokos. Separating polynomial invariants over non-closed fields of finite abelian groups. Applied and Computational Harmonic Analysis, 84:101877, 2026. arXiv:2506.22889v1; DOI: 10.1016/j.acha.2026.101877.DOI
  8. [8]F. Alberto Grünbaum and Calvin C. Moore. The use of higher-order invariants in the determination of generalized Patterson cyclotomic sets. Acta Crystallographica Section A, 51(3):310–323, 1995.DOI
  9. [9]David J. Grynkiewicz. Structural Additive Theory, volume 30 of Developments in Mathematics. Springer, Cham, 2013.
  10. [10]Jing Huang. The separating noether number of finite abelian groups, 2026. arXiv:2603.23164v1.arxiv.org/abs/2603.23164
  11. [11]Dongchun Han, Xuan Wang, Hanbin Zhang, and Shiwen Zhang. On zero-sum polytopes: Reciprocity, rigidity, and cyclic sieving, 2026. arXiv:2606.11005v1.arxiv.org/abs/2606.11005
  12. [12]Ramakrishna Kakarala and Geoffrey J. Iverson. Uniqueness results for multiple correlations of periodic functions. Journal of the Optical Society of America A, 10(7):1517–1528, 1993.DOI
  13. [13]Tamás Keleti and Mihail N. Kolountzakis. On the determination of sets by their triple correlation in finite cyclic groups. Online Journal of Analytic Combinatorics, 1:1–18, 2006. Paper 4; arXiv:math/0603415v1; DOI: 10.61091/ojac-104.DOI
  14. [14]Sergei V. Konyagin and Vsevolod F. Lev. Combinatorics and linear algebra of Freiman’s isomorphism. Mathematika, 47(1–2):39–51, 2000.DOI
  15. [16]John A. McLaughlin and Josef Raviv. Nth-Order Autocorrelations in Pattern Recognition. Information and Control, 12(2):121–142, 1968.
  16. [17]Luke Pebody. The reconstructibility of finite abelian groups. Combinatorics, Probability and Computing, 13(6):867–892, 2004. DOI: 10.1017/S0963548303005807.DOI
  17. [18]Luke Pebody. Reconstructing odd necklaces. Combinatorics, Probability and Computing, 16(4):503–514, 2007. DOI: 10.1017/S0963548306007875.DOI
  18. [19]Jan Simon. Reconstructing Colourings of Finite Groups. PhD thesis, RWTH Aachen University, 2017. DOI: 10.18154/RWTH-2017-07674.DOI

Paper details

vlnc:W_bent7gm9
v1 · latestHistory (1)

published · Fresh — published within the last 30 days

Usage

views · 1

downloads · 0

A view counts once per browser per day, a download each time the PDF is requested.

CC BY 4.0

Original source

  • Mathematics

OpenAI Codex GPT-5.6 Sol · View statement →

Looking for related papers…
Contents