ISSN 2148-838Xhttps://doi.org/10.13069/jacodesmath.1056624 J. Algebra Comb. Discrete Appl. 9(1) • 57–70 Received: 11 July 2021 Accepted: 8 October 2021 Journal of Algebra Combinatorics Discrete Structures and Applications 1-generator two-dimensional quasi-cyclic codes over Z4[u]/〈u2 −1〉 Research Article Arazgol Ghajari, Kazem Khashyarmanesh, Zohreh Rajabi Abstract: In this paper, we obtain generating set of polynomials of two-dimensional cyclic codes over the ring R = Z4[u]/〈u2−1〉, where u2 = 1. Moreover, we find generator polynomials for two-dimensional quasi- cyclic codes and two-dimensional generalized quasi-cyclic codes over R and specify a lower bound on minimum distance of free 1-generator two-dimensional quasi-cyclic codes and two-dimensional generalized quasi-cyclic codes over R. 2010 MSC: 12E20, 94B05, 94B15, 94B60 Keywords: Two-dimensional cyclic codes, Two-dimensional quasi-cyclic codes, Two-dimensional generalized quasi-cyclic codes 1. Introduction There are many generalizations of cyclic codes. One of them is two-dimensional cyclic codes. A lot of works on two-dimensional cyclic codes has done. Ikai et al. first introduced the concept of common zeros for characterizing two-dimensional codes [6], and showed the existence of two-dimensional codes that can be characterized by the common zeros. After that the researchers have studied with different concepts in these codes. The reader can find some of such studies in the papers [11–13]. Moreover, Lalason et al. [7] construct a basis of an s-dimensional cyclic code over a finite field. On the other hand, quasi-cyclic codes are another natural generalizations of cyclic codes. The study of quasi-cyclic codes over finite rings has provided useful information in coding theory. We shall use the phrase ‘QC code’ as an abbreviation for ‘quasi-cyclic code’ and ‘GQC code’ for ‘generalized quasi-cyclic codes’. QC codes form an important class of linear codes which also include cyclic codes (when we consider the case ` = 1). Ling and Solé studied the algebraic structure of QC codes over finite fields and provided a new algebraic approach to QC codes (see also [8]). There have been a lot of investigations of QC codes and GQC codes over Arazgol Ghajari, Kazem Khashyarmanesh (Corresponding Author), Zohreh Rajabi; Department of Pure Math- ematics, Ferdowsi University of Mashhad, Mashhad, Iran (email: Ghajari3051@gmail.com, khashyar@ipm.ir, rajabi261@yahoo.com). 57 https://orcid.org/0000-0002-3675-2832 https://orcid.org/0000-0003-3314-7298 https://orcid.org/0000-0001-7857-2672 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 the rings, for example [1–3, 5, 9, 14]. In [10], the authors studied the constacyclic codes over the finite non-chain ring Z4 + uZ4 with u2 = 1 and obtained some new Z4-linear codes. Finally, Gao et al. [4] have generalized QC codes and GQC codes over the finite non-chain ring R = Z4[u]/〈u2 − 1〉 with u2 = 1. They have determined the structure of the generators and the minimal generating sets of 1-generator QC codes and GQC codes. They also have given a lower bound on minimum distance of free 1-generator QC codes and GQC codes over R. Furthermore, in [4], some new Z4-linear codes were constructed by 1-generated QC codes and GQC codes over R. Hence, there are many examples of cyclic codes and QC codes over R. There exist many researches of two-dimensional cyclic codes over finite fields. However, the research of two-dimensional cyclic codes over R has not been considered by any coding scientist. Moreover, quasi-cyclic codes perform very well on the codes have great lengths. Therefore, these codes are the important and most intensively studies classes of linear codes. The ring R = Z4[u]/〈u2 − 1〉 with u2 = 1 is a Frobenius non-chain ring with 16 elements. There are some examples of cyclic codes over R whose Z4 Gray images have better parameters than previous best-known Z4-linear codes were presented (see for example [4] and [10]). The main purpose of this paper is to obtain sets of generator polynomials of two-dimensional cyclic codes over R. We also determine the structure of the generators and the minimal generating sets of 1-generator two-dimensional QC codes and two-dimensional GQC codes. This method probably helps to decode two-dimensional cyclic codes and two-dimensional QC codes as it has done for cyclic codes and QC codes. This paper is organized as follows: at first, we find the generator polynomials corresponding to two-dimensional cyclic codes over R. Then, by using these polynomials, we obtain generator polynomials for two-dimensional QC codes over R. Moreover, we study the structure of generators two-dimensional QC codes. The last part of the paper is devoted to obtain 1-generator polynomial two-dimensional GQC codes and determine a lower bound for the minimum distance of free 1-generator GQC codes. 2. Generator polynomials As was mentioned in the Introduction, the purpose of this section is to obtain a generating set of polynomials for two-dimensional QC codes over the ring R = Z4[u]/ < u2 − 1 > with u2 = 1. Assume that S := Z4[x]/ < xm − 1 >, R′ := R[x,y]/ < xm − 1,y3 − 1 >, where y3 = 1, xm = 1 and m is an odd positive integer. Suppose that n = 3m` and R := R ′`. As before, Fq denotes a finite field with q elements. Recall that a linear code C′ of length ms over a finite field F is a two-dimensional cyclic code, if it is closed under row shift and column shift of codewords, whose codewords are viewed as ms arrays. This means that for every codeword c of the form c =   c0,0 c0,1 · · · c0,s−1 c1,0 c1,1 · · · c1,s−1 ... ... ... cm−1,0 cm−1,1 · · · cm−1,s−1   in C′, the codewords   cm−1,0 cm−1,1 · · · cm−1,s−1 c0,0 c0,1 · · · c0,s−1 ... ... ... cm−2,0 cm−2,1 · · · cm−2,s−1   and   c0,s−1 c0,0 · · · c0,s−2 c1,s−1 c1,0 · · · c1,s−2 ... ... ... cm−1,s−1 cm−1,01 · · · cm−1,s−2   58 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 also belong to C′. It is well known that these codes are the ideals of the quotient ring F [x,y]/ < xm − 1,ys − 1 >. Similarly, we consider the above definition for a two-dimensional cyclic code C′ of length ms over the ring R. So we define a two-dimensional QC codes over R as follows. Definition 2.1. Let C be a linear code of length n. If there exists a least positive integer ` such that C is closed the `th composition under the row shift and the column shift, then we call C is a two-dimensional QC code over R. Clearly, ` is a divisor of n. If ` = 1, then C is a two-dimensional cyclic code over R. An r-generator two-dimensional QC code is an ideal of C with r generators. In the rest of this section, we shall focus on 1-generator two-dimensional QC code over R. According to Gao et al.[3], 1-generator two-dimensional QC code C over R can be generated by element (b1(x,y), . . . ,b`(x,y)) ∈R, and so C = {f(x,y)(b1(x,y), . . . ,b`(x,y))|f(x,y) ∈ R[x,y]} = {(f(x,y)b1(x,y), . . . ,f(x,y)b`(x,y))|f(x,y) ∈ R[x,y]}. Özen et al.[10] have studied cyclic codes over R. In fact, they determined a generators of the cyclic codes over R. In [10], it was proved that if m is odd, then S is a principal ideal ring. Now, by using a method similar that used for two-dimensional cyclic codes over a field in [13], we obtain a generator polynomials for two-dimensional cyclic codes over R. Our generating set has an important role in determining generator polynomials two-dimensional QC codes over R. Note that R is isomorphic to Z4 + uZ4. We begin with the following lemma. Lemma 2.2. Suppose that C′ is a two-dimensional cyclic code of length 3m over R. Then {pi(x,y) | i = 1, . . . , 6 } is a generating set of C′, where p1(x,y) =α01(x) + (u + 1)α11(x) + (β01(x) + (u + 1)β11(x))y + (γ01(x) + (u + 1)γ11(x))y 2, p2(x,y) =(u + 1)α12(x) + (β02(x) + (u + 1)β12(x))y + (γ02(x) + (u + 1)γ12(x))y 2, p3(x,y) =(β03(x) + (u + 1)β13(x))y + (γ03(x) + (u + 1)γ13(x))y 2, p4(x,y) =(u + 1)β14(x)y + (γ04(x) + (u + 1)γ14(x))y 2, p5(x,y) =(γ05(x) + (u + 1)γ15(x))y 2, p6(x,y) =(u + 1)γ16(x)y 2, and α0i(x), α1i(x), β0i(x), β1i(x),γ0i(x) and γ1i(x) are generator polynomials of cyclic codes over Z4 for each i = 1, . . . , 6. Proof. Suppose that I is an ideal of R′ and that f(x,y) is an arbitrary element of I. So it can be written uniquely as the following form f(x,y) = f0(x) + (u + 1)f1(x) + (f ′ 0(x) + (u + 1)f ′ 1(x))y + (f ′′ 0 (x) + (u + 1)f ′′ 1 (x))y 2, where f0(x), f′0(x), f ′′ 0 (x), f1(x), f ′ 1(x) and f ′′ 1 (x) are polynomials in S. The main strategy employed in our proof is to introduce six auxiliary ideals in S. To achieve this, we break our proof into six steps as follows: Step 1: Set I0 := {g0(x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) =g0(x) + (u + 1)g1(x) + (g ′ 0(x) + (u + 1)g ′ 1(x))y + (g ′′ 0 (x) + (u + 1)g ′′ 1 (x))y 2, where g1(x),g ′ 0(x),g ′ 1(x),g ′′ 0 (x),g ′′ 1 (x) ∈ S}. 59 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 It is not hard to see that the set I0 is an ideal of S. Since m is odd, S is a principal ideal ring. Thus, there exists a polynomial α01(x) in S such that I0 = 〈α01(x)〉. Since α01 is an element of I0, according to the definition of I0, there exists p1(x,y) ∈ I with p1(x,y) = α01(x) + (u + 1)α11(x) + (β01(x) + (u + 1)β11(x))y + (γ01(x) + (u + 1)γ11(x))y 2, where α01(x), α11(x), β01(x), β11(x), γ01(x), γ11(x) ∈ S. It is clear that f0(x) ∈ I0. Hence there exists t0(x) ∈ Z4[x] such that f0(x) = α01(x)t0(x). Set h1(x,y) :=f(x,y) −p1(x,y)t0(x) =(u + 1)h01(x) + (h ′ 01(x) + (u + 1)h ′ 11(x))y + (h ′′ 01(x) + (u + 1)h ′′ 11(x))y 2, where h01(x), h′01(x), h ′ 11(x), h ′′ 01(x), h ′′ 11(x) ∈ S. Since f(x,y) and p1(x,y) are in I and I is an ideal of R, h1(x,y) is again in I. Step 2: Put I′0 := {g1(x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) =(u + 1)g1(x) + (g ′ 0(x) + (u + 1)g ′ 1(x))y + (g ′′ 0 (x) + (u + 1)g ′′ 1 (x))y 2, where g′0(x),g ′ 1(x),g ′′ 0 (x),g ′′ 1 (x) ∈ S}. Clearly, I′0 is an ideal of S. Thus, there exists a polynomial α12(x) ∈ S such that I′0 = 〈α12(x)〉. There exists p2(x,y) ∈ I such that p2(x,y) = (u + 1)α12(x) + (β02(x) + (u + 1)β12(x))y + (γ02(x) + (u + 1)γ12(x))y 2, where β02(x), β12(x), γ02(x), γ12(x) ∈ S. According to the definition of I′0, h01(x) ∈ I′0, and so h01(x) = α12(x)t1(x) for some t1(x) ∈ Z4[x]. Set h2(x,y) :=h1(x,y) −p2(x,y)t1(x) =(h′02(x) + (u + 1)h ′ 12(x))y + (h ′′ 02(x) + (u + 1)h ′′ 12(x))y 2, where h′02(x), h ′ 12(x), h ′′ 02(x), h ′′ 12(x) ∈ S. Since h1(x,y) and p2(x,y) are polynomials in I we have that h2(x,y) ∈ I. Step 3: Set I1 := {g′0(x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) =(g′0(x) + (u + 1)g ′ 1(x))y + (g ′′ 0 (x) + (u + 1)g ′′ 1 (x))y 2, where g′1(x),g ′′ 0 (x),g ′′ 1 (x) ∈ S}. Obviously, I1 is an ideal of S, and so there exists a polynomial β03(x) in S such that I1 = 〈β03(x)〉. There exists a polynomial p3(x,y) ∈ I such that p3(x,y) = (β03(x) + (u + 1)β13(x))y + (γ03(x) + (u + 1)γ13(x))y 2, where β13(x), γ03(x), γ13(x) ∈ S. According to the definition of I1, h′02(x) in I1. Hence h′02(x) = β03(x)t2(x) for some t2(x) ∈ Z4[x]. Put h3(x,y) :=h2(x,y) −p3(x,y)t2(x) =(u + 1)h′13(x)y + (h ′′ 03(x) + (u + 1)h ′′ 13(x))y 2, where h′13(x), h ′′ 03(x), h ′′ 13(x) ∈ S. Similar to the previous discussion h3(x,y) ∈ I. 60 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Step 4: Set I′1 := {g′1(x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) = (u + 1)g′1(x)y + (g ′′ 0 (x) + (u + 1)g ′′ 1 (x))y 2, where g′′0 (x),g ′′ 1 (x) ∈ S}. It is clear that I′1 is an ideal of S. Thus, there exists a polynomial β13(x) ∈ S such that I′1 = 〈β13〉. Since β13(x) in I′1, according to definition I ′ 1, we have a polynomial p4(x,y) ∈ I, where p4(x,y) = (u + 1)β13(x)y + (γ03(x) + (u + 1)γ13(x))y 2, and γ03(x), γ13(x) ∈ S. Obviously, h′13(x) ∈ I′1. So, we get h′13(x) = β13(x)t3(x) for some t3(x) ∈ Z4[x]. Put h4(x,y) := h3(x,y) −p4(x,y)t3(x) = (h04(x) + (u + 1)h14(x))y2, where h04(x), h14(x) ∈ S. It is clear that h4(x,y) ∈ I. Step 5: Set I2 := {g′′0 (x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) = (g′′0 (x) + (u + 1)g ′′ 1 (x))y 2, where g′′1 (x) ∈ S}. Clearly, I2 is an ideal of S. Therefore, there exists γ05(x) ∈ S such that I2 = 〈γ05(x)〉. Besides, γ05(x) in I2, and so we have a polynomial p5(x,y) ∈ I, where p5(x,y) = (γ05(x) + (u + 1)γ15(x))y 2, where γ15(x) ∈ S. Obviously, h04(x) ∈ I2, and so we obtain that h04(x) = γ05(x)t4(x) for some t4(x) ∈ Z4[x]. Put h5(x,y) := h4(x,y)−p5(x,y)t4(x) = (u + 1)h05(x)y2, where h05(x) ∈ S. Similarly, h5(x,y) in I. Step 6: Put I′2 := {g ′′ 1 (x) ∈ S : there exists g(x,y) ∈ I such that g(x,y) = (u + 1)g ′′ 1 (x)y 2}. It is clear that I′2 is an ideal of S. Thus there exists γ15(x) ∈ S such that I′2 =< γ15(x) >. Also there exists a polynomial p6(x,y) ∈ I such that p6(x,y) = (u + 1)γ15(x)y2. Now, since h05 ∈ I′2, there exists t5(x) ∈ S such that h05(x) = γ15(x)t5(x). Therefore, h5(x,y) = (u + 1)γ15(x)t5(x)y2 = p6(x,y)t5(x). Now, we get f(x,y) = h1(x,y) + p1(x,y)t0(x), h1(x,y) = h2(x,y) + p2(x,y)t1(x), h2(x,y) = h3(x,y) + p3(x,y)t2(x), h3(x,y) = h4(x,y) + p4(x,y)t3(x), h4(x,y) = h5(x,y) + p5(x,y)t4(x), h5(x,y) = p6(x,y)t5(x). These equality imply that f(x,y) = p1(x,y)t0(x) + p2(x,y)t1(x) + p3(x,y)t2(x) + p4(x,y)t3(x) + p5(x,y)t4(x) + p6(x,y)t5(x). Thus I = 〈p1(x,y),p2(x,y),p3(x,y),p4(x,y),p5(x,y),p6(x,y)〉. 61 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Now, we state an important lemma. Lemma 2.3. Let C be a 1-generator two-dimensional QC code of length n = 3m` which is generated by G(x,y) = (G1(x,y),G2(x,y), . . . ,G`(x,y)) ∈ R, where Gi(x,y) ∈ R′ for all i with 1 ≤ i ≤ `. Then Gi(x,y) ∈ Ci, where Ci is a two-dimensional cyclic code of length m over R. Furthermore, if m is odd, then Gi(x,y) can be selected as the form Gi(x,y) = ϕ0i(x) + (u + 1)ϕ1i(x) + (ψ0i(x) + (u + 1)ψ1i(x))y + (θ0i(x) + (u + 1)θ1i(x))y 2, where ϕ0i(x), ϕ1i(x), ψ0i(x), ψ1i(x), θ0i(x) and θ1i(x) are polynomials in R[x] for all i with 1 ≤ i ≤ ` and moreover, ϕ0i(x), ψ0i(x) and θ0i(x) are monic polynomials for all i = 1, · · · ,`. Proof. Consider the projection map ψi : R→ R′ given by ψi(k1(x,y), . . . ,k`(x,y)) = ki(x,y), where ki(x,y) ∈ R′ for all i = 1, · · · ,`. It is clear that the set ψi(C) is a two-dimensional cyclic code over R for all i with 1 ≤ i ≤ `. Now, in view of Lemma 2.2, for all 1 ≤ i ≤ `, one can obtain a generator for ψi(C) as follows ψi(C) = 〈p1i(x,y),p2i(x,y),p3i(x,y),p4i(x,y),p5i(x,y),p6i(x,y)〉, where, for each j = 1, . . . , 6, pji(x,y) are polynomials as described in Lemma 2.2 . Since Gi(x,y) ∈ ψi(C) for all 1 ≤ i ≤ `, there exists a polynomial fi(x,y) ∈ R[x,y] such that Gi(x,y) = fi(x,y)(α i 01(x) + (u + 1)α i 11(x) + (β i 01(x) + (u + 1)β i 11(x))y + (γi01(x) + (u + 1)γ i 11(x))y 2) = ϕ0i(x) + (u + 1)ϕ1i(x) + (ψ0i(x) + (u + 1)ψ1i(x))y + (θ0i(x) + (u + 1)θ1i(x))y 2, where αi01(x), α i 11(x), β i 01(x), β i 11(x), γ i 01(x) and γ i 11(x) are generator polynomials of cyclic codes over Z4 and, for all 1 ≤ i ≤ `, ϕ0i(x), ϕ1i(x), ψ0i(x), ψ1i(x), θ0i(x) and θ1i(x) are polynomials in R[x]. Moreover, ϕ0i(x), ψ0i(x) and θ0i(x) are monic polynomials for all i = 1, · · · ,`. In the light of the above two lemmas, we will obtain the minimal generating sets for 1-generator two-dimensional QC codes. Theorem 2.4. Let C be a 1-generator two-dimensional QC code of length n = 3m` over R which is generated by G = (G1(x,y),G2(x,y), . . . ,G`(x,y)), with m is odd and Gi(x,y) = ϕ0i(x) + (u + 1)ϕ1i(x) + (ψ0i(x) + (u + 1)ψ1i(x))y + (θ0i(x) + (u + 1)θ1i(x))y 2, where ϕ0i(x), ϕ1i(x), ψ0i(x), ψ1i(x), θ0i(x) and θ1i(x) are polynomials in R[x] for all i with 1 ≤ i ≤ ` and moreover, ϕ0i(x), ψ0i(x) and θ0i(x) are monic polynomials for all 1 ≤ i ≤ `. Assume that deg(ϕ0i(x)) >deg(ϕ1i(x)), deg(ψ0i(x)) >deg(ψ1i(x)) and deg(θ0i(x)) >deg(θ1i(x)), for all 1 ≤ i ≤ `, and that the polynomials ϕ0i(x) + (u + 1)ϕ1i(x), (ψ0i(x) + (u + 1)ψ1i(x))y and (θ0i(x) + (u + 1)θ1i(x))y2 are not zero divisor in R′. Assume that g0(x) = gcd{ϕ01(x),ϕ02(x), . . . ,ϕ0`(x)}, q0(x) = gcd{ϕ11(x),ϕ12(x), . . . ,ϕ1`(x)}, g1(x) = gcd{ψ01(x),ψ02(x), . . . ,ψ0`(x)}, q1(x) = gcd{ψ11(x),ψ12(x), . . . ,ψ1`(x)}, g2(x) = gcd{θ01(x),θ02(x), . . . ,θ0`(x)}, q2(x) = gcd{θ11(x),θ12(x), . . . ,θ1`(x)} 62 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 and, for k = 0, 1, 2, gk(x)|xm − 1 and qk(x)|xm − 1. Let S1 = r0−1⋃ j=0 {xj(ϕ01(x) + (u + 1)ϕ11(x), . . . ,ϕ0`(x) + (u + 1)ϕ1`(x))}, S2 = r1−1⋃ j=0 {xj((ψ01(x) + (u + 1)ψ11(x))y, . . . , (ψ0`(x) + (u + 1)ψ1`(x))y)}, S3 = r2−1⋃ j=0 {xj((θ01(x) + (u + 1)θ11(x))y2, . . . , (θ0`(x) + (u + 1)θ1`(x))y2)}, S4 = t0−1⋃ j=0 {xj((u + 1)h0ϕ11(x), . . . , (u + 1)h0ϕ1`(x))}, S5 = t1−1⋃ j=0 {xj((u + 1)h1ψ11(x)y, . . . , (u + 1)h1ψ1`(x)y)}, S6 = t2−1⋃ j=0 {xj((u + 1)h2θ11(x)y2, . . . , (u + 1)h2θ1`(x)y2)}, where, for all k = 0, 1, 2, we set rk := deg(x m−1 gk(x) ) and tk := deg(x m−1 qk(x) ). Then S1 ∪S2 ∪S3 ∪S4 ∪S5 ∪S6 is a minimal generating set for C. Moreover, | C |= 16r0+r1+r2 4t0+t1+t2 for all 1 ≤ i ≤ `. Proof. For k = 0, 1, 2, put hk(x) := x m−1 gk(x) and δk(x) := x m−1 qk(x) , and let c(x,y) = f(x,y)G be a codeword in C, where f(x,y) = f0(x) + f1(x)y + f2(x)y2, with fi(x) ∈ R[x] for all 1 ≤ i ≤ 3. For simplicity of presentation, in our proof, we will use the notion f instead of f(x). By the division algorithm, we get the unique polynomials Q0(x), Q1(x), Q2(x), R0(x), R1(x), R2(x) in R[x] such that f0 = h0Q0 + R0, where R0 = 0 or deg(R0) < r0, f1 = h1Q1 + R1, where R1 = 0 or deg(R1) < r1, f2 = h2Q2 + R2, where R2 = 0 or deg(R2) < r2. There exist polynomials ai, a′i, a ′′ i ∈ Z4[x] such that h0ϕ0i = h0g0ai = 0, h1ψ0i = h1g1a ′ i = 0, h2θ0i = h2g2a ′′ i = 0 for all 1 ≤ i ≤ `. We have c(x,y) = f(x,y)G = (h0Q0 + R0)(ϕ01 + (u + 1)ϕ11, . . . ,ϕ1` + (u + 1)ϕ1`) + (h1Q1 + R1)((ψ01 + (u + 1)ψ11)y, . . . , (ψ0` + (u + 1)ψ1`)y) + (h2Q2 + R2)((θ01 + (u + 1)θ11)y 2, . . . , (θ0` + (u + 1)θ1`)y 2) = Q0h0((u + 1)ϕ11, . . . , (u + 1)ϕ1`) + R0(ϕ01 + (u + 1)ϕ11, . . . ,ϕ0` + (u + 1)ϕ1`) + Q1h1((u + 1)ψ11y, . . . , (u + 1)ψ1`y) + R1((ψ01 + (u + 1)ψ11)y, . . . , (ψ0` + (u + 1)ψ1`)y) + Q2h2((u + 1)θ11y 2, . . . , (u + 1)θ1`y 2) + R2((θ01 + (u + 1)θ11)y 2, . . . , (θ0` + (u + 1)θ1`)y 2). They are not difficult to verify that R0(ϕ01 + (u + 1)ϕ11, . . . ,ϕ0` + (u + 1)ϕ1`) ∈Span(S0), R1((ψ01 + (u + 1)ψ11)y, . . . , (ψ0` + (u + 1)ψ1`)y) ∈Span(S1), and R2((θ01 + (u + 1)θ11)y 2, . . . , (θ0` + (u + 1)θ1`)y 2) ∈Span(S2). 63 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Again, using the division algorithm, we get the unique polynomials Q′0(x),Q ′ 1(x), Q′2(x),R ′ 0(x),R ′ 1(x), R ′ 2(x) ∈ R[x] such that Q0 = δ0Q ′ 0 + R ′ 0, where R ′ 0 = 0 or deg(R ′ 0) < t0, Q1 = δ1Q ′ 1 + R ′ 1, where R ′ 1 = 0 or deg(R ′ 1) < t1, and Q2 = δ2Q ′ 2 + R ′ 2, where R ′ 2 = 0 or deg(R ′ 2) < t2. There exist polynomials bi, b′i, b ′′ i ∈ Z4[x] such that δ0Q ′ 0(u + 1)h0ϕ1i = (u + 1)Q ′ 0q0δ0bi = 0, δ1Q ′ 1(u + 1)h1ψ1i = (u + 1)Q ′ 1q1δ1b ′ i = 0, and δ2Q ′ 2(u + 1)h2θ1i = (u + 1)Q ′ 2q2δ2b ′′ i = 0 in R′ for all 1 ≤ i ≤ `. It is not hard to see that Q0((u + 1)h0ϕ11, . . . , (u + 1)h0ϕ1`) = R ′ 0((u + 1)h0ϕ11, . . . , (u + 1)h0ϕ1`) ∈ Span(S4), Q1((u + 1)h1ψ11y, . . . , (u + 1)h1ψ1`y) = R ′ 1((u + 1)h1ψ11y, . . . , (u + 1)h1ψ1`y) ∈ Span(S5), and Q2((u + 1)h2θ11y 2, . . . , (u + 1)h2θ1`y 2) = R′2((u + 1)h2θ11y 2, . . . , (u + 1)h2θ1`y 2) ∈ Span(S6). Thus S1∪S2∪S3∪S4∪S5∪S6 is a Spanning set for C. Also, it is clear S1∩S2∩S3∩S4∩S5∩S6 = {0}. With the aid of the above theorem, we obtain the following corollary. Corollary 2.5. If ` is a positive integer and ϕ1i(x) = xm −1, ψ1i(x) = xm −1 and θ1i(x) = xm −1 are polynomials over R, for all i with 1 ≤ i ≤ `, then C is a free two-dimensional QC code of rank r0 +r1 +r2 over R and its minimal generating set is S1 ∪S2 ∪S3 such that S1 = r0−1⋃ j=0 {xj(ϕ01(x), . . . ,ϕ0`(x))}, S2 = r1−1⋃ j=0 {xj(ψ01(x)y, . . . ,ψ0`(x)y)}, S3 = r2−1⋃ j=0 {xj(θ01(x)y2, . . . ,θ0`(x)y2)}, where, for all k = 0, 1, 2, we set rk := deg(x m−1 gk(x) ). Furthermore, | C |= 16r0+r1+r2 . Proof. By Theorem 2.4, if ϕ1i(x) = xm − 1, ψ1i(x) = xm − 1 and θ1i(x) = xm − 1 are polynomials over R, for all i with 1 ≤ i ≤ `, then q0 =gcd{ϕ11(x), . . . ,ϕ1`(x),xm − 1} = xm − 1, q1 =gcd{ψ11(x), . . . ,ψ1`(x),xm − 1} = xm − 1, and q2 =gcd{θ11(x), . . . ,θ1`(x),xm − 1} = xm − 1. Hence δ0 = 1, δ1 = 1 and δ2 = 1. Clearly, S1 ∩ S2 ∩ S3 = {0}. Therefore, its minimal generating set is S1 ∪ S2 ∪ S3. This means that C is a free two-dimensional QC code of rank r0 + r1 + r2. Thus | C |= 16r0+r1+r2. In the next theorem, we provide a lower bound on minimum distance of the free 1-generator two- dimensional QC codes over R. 64 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Theorem 2.6. Let C be a free 1-generator two-dimensional QC code of length n = 3m` over R as in Corollary 2.5. Suppose that h0i =(x m − 1)/ϕ0i(x), h1i = (xm − 1)/ψ0i(x), h2i =(x m − 1)/θ0i(x), h0 = lcm{h01, . . . ,h0`}, h1 =lcm{h11, . . . ,h1`} and h2 = lcm{h21, . . . ,h2`} for all i with 1 ≤ i ≤ `. Then we have the following statements. (i) dmin(C) ≥ ∑ i/∈A d0i + ∑ j/∈B d1j + ∑ t/∈D d2t for all 1 ≤ i,j,t ≤ `, where A,B,C ⊆{1, 2, . . . ,`} are sets from maximum size for which lcm{h0i, i ∈ A} 6= h0, lcm{h1j,j ∈ B} 6= h1 and lcm{h2t, t ∈ D} 6= h2. (ii) If h01 = h02 = . . . = h0`, h11 = h12 = . . . = h1` and h21 = h22 = . . . = h2`, then dmin(C) ≥ ∑̀ i=1 d0i + ∑̀ i=1 d1i + ∑̀ i=1 d2i. Proof. (i) Consider the projection map ψi : R→ R′ given by ψi(k1(x,y), . . . ,k`(x,y)) = ki(x,y), where ki(x,y) ∈ R′ for all i with 1 ≤ i ≤ `. It is easy to show that ψi(C) is a two-dimensional code over R. Let c(x,y) = f(x,y)G be a nonzero codeword in C, where f(x,y) ∈ R[x,y]. Since C is a free 1-generator two-dimensional QC code, we have that ϕ1i(x) = xm − 1, ψ1i(x) = xm − 1, θ1i(x) = xm − 1 for all 1 ≤ i ≤ `. So, the i-th component is zero if and only if (xm − 1) | f(x,y)G. This means that (xm−1) | f0(x)ϕ0i(x), (xm−1) | f1(x)ψ0i(x) and (xm−1) | f2(x)θ0i(x), that is, if and only if h0i | f0(x), h1i | f1(x), h2i | f2(x) for all 1 ≤ i ≤ `. Thus c(x,y) = 0 if and only if h0 | f0(x), h1 | f1(x) and h2 | f2(x). Therefore, c(x,y) 6= 0 if and only if h0 - f0(x) or h1 - f1(x) or h2 - f2(x). Thus, c(x,y) 6= 0 have the most number of zero blocks whenever h0 6= lcm{h0i, i ∈ A}, where lcm{h0i, i ∈ A} | f0(x), h1 6= lcm{h1j,j ∈ B}, where lcm{h1j,j ∈ B} | f1(x), h2 6= lcm{h2t, t ∈ D}, where lcm{h2t, t ∈ D} | f2(x), where A, B and D are a maximal subset of {1, 2, . . . ,`} having this property. Thus dmin(C) ≥ ∑ i/∈A d0i + ∑ i/∈B d1i + ∑ i/∈D d2i. (ii) Now, we know that A = ∅ if and only if h01 = h02 = . . . = h0` and also, B = ∅ if and only if h11 = h12 = . . . = h1`. Moreover, D = ∅ if and only if h21 = h22 = . . . = h2`. Thus, dmin(C) ≥ ∑` i=1 d0i + ∑` i=1 d1i + ∑` i=1 d2i. Corollary 2.7. Let C be a 1-generator two-dimensional QC code of length n = 3m` over R which is generated by G = (ϕ01(x) + (u + 1)ϕ11(x) + (ψ01(x) + (u + 1)ψ11(x))y+ (θ01(x) + (u + 1)θ11(x))y 2, . . . ,ϕ0`(x) + (u + 1)ϕ1`(x)+ (ψ0`(x) + (u + 1)ψ1`)y + (θ0`(x) + (u + 1)θ1`(x))y 2), 65 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 where m is odd. Assume that ϕ1i(x) = xm−1, ψ1i(x) = xm−1 and θ1i(x) = xm−1 for each i = 1, 2, . . . ,`. Let h0i = (xm − 1)/ϕ0i(x), h1i = (xm − 1)/ψ0i(x) and h2i = (xm − 1)/θ0i(x), for all i with 1 ≤ i ≤ `, and that h0 = lcm{h01,h02, . . . ,h0`}, h1 = lcm{h11,h12, . . . ,h1`}, and h2 = lcm{h21,h22, . . . ,h2`}. Then (i) C is a free two-dimensional QC code from deg(h0)+ deg(h1)+ deg(h2). Moreover, | C |= 16deg(h0)+deg(h1)+deg(h2). (ii) dmin(C) ≥ ∑ i/∈A d0i + ∑ i/∈B d1i + ∑ i/∈D d2i, where A,B,D ⊆{1, 2, . . . ,`} are set from maximum size for which lcm{h0i, i ∈ A} 6= h0, lcm{h1j,j ∈ B} 6= h1 and lcm{h2t, t ∈ D} 6= h2. (iii) If h01 = h02 = . . . = h0`, h11 = h12 = . . . = h1` and h21 = h22 = . . . = h2`, then dmin(C) ≥ ∑̀ i=1 d0i + ∑̀ i=1 d1i + ∑̀ i=1 d2i. Proof. Let c(x,y) = f(x,y)G be a codeword in C such that f(x,y) = f0(x) + f1(x)y + f2(x)y2, where fi(x) ∈ R[x] for i = 0, 1, 2. By the division algorithm, we can find unique polynomials Q1(x),Q2(x),Q3(x),R1(x),R2(x), R3(x) ∈ R[x] such that f0(x) = h0Q1(x) + R1(x), where R1(x) = 0, or degR1(x) < deg(h0), f1(x) = h1Q2(x) + R2(x), where R2(x) = 0, or degR2(x) < deg(h1), f2(x) = h2Q2(x) + R3(x), where R3(x) = 0, or degR3(x) < deg(h2). Now, we have c(x,y) = f(x,y)G = (h0Q1(x) + R1(x))(ϕ01(x), . . . ,ϕ0`(x)) + (h1Q2(x) + R2(x))(ψ01(x)y, . . . ,ψ0`(x)y) + (h2Q3(x) + R3(x))(θ01(x)y 2, . . . ,θ0`(x)y 2). We know that h0ϕ0i(x) = h1ψ0i(x) = h2θ0i(x) = xm − 1. Therefore, we obtain R1(x)(ϕ01(x), . . . ,ϕ0`(x)) ∈ Span(S1), R2(x)(ψ01(x)y, . . . ,ψ0`(x)y) ∈ Span(S2) and R3(x)(θ01(x)y 2, . . . ,θ0`(x)y 2 ∈ Span(S3). Thus t0 = 0, t1 = 0 and t2 = 0 which implies that S4 = S5 = S6 = ∅. Using the definition of free module, we obtain C is a free two-dimensional QC code of rank deg(h0) + deg(h1) + deg(h2). Therefore, | C |= 16deg(h0)+deg(h1)+deg(h2). The statements (ii) and (iii) follow from Theorem 2.6. 66 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 3. 1-generator two-dimensional GQC codes In this section, we study two-dimensional GQC codes over R. At first, we recall the definition of 1-generator two-dimensional GQC codes over R. Definition 3.1. Let m1, m2, . . . ,m` be positive integers and Ri = R[x,y]/〈xmi − 1,y3 − 1〉 for all i with 1 ≤ i ≤ `. Any ideal of R = R1 ×R2 × . . .×R` is called a two-dimensional GQC code of length (m1,m2, . . . ,m`) with index ` over R. If C is a two-dimensional GQC code of length (m1,m2, . . . ,m`) with m = m1 = . . . = m`, then C is a two-dimensional QC code with length n = 3m`. Lemma 3.2. Let C be a 1-generator two-dimensional GQC code of length (m1, . . . ,m`) and G′(x,y) = (G′1(x,y),G ′ 2(x,y), . . . ,G ′ `(x,y)) ∈ R be a generator of C, where G ′ i(x,y) ∈ Ri for all i with 1 ≤ i ≤ `. Then G′i(x,y) ∈ Ci, where Ci is a two-dimensional cyclic code of length mi over R for i = 1, · · · ,`. Also, if mi is odd, then G′i(x,y) can be selected to be of the form G ′ i(x,y) = (ϕ0i(x) + (u+ 1)ϕ1i(x) + (ψ0i(x) + (u + 1)ψ1i(x))y + (θ0i(x) + (u + 1)θ1i(x))y 2) where ϕ0i(x), ϕ1i(x), ψ0i(x), ψ1i(x), θ0i(x) and θ1i(x) are polynomials in R[x] for all i with 1 ≤ i ≤ `. Furthermore, ϕ0i(x), ψ0i(x) and θ0i(x) are monic polynomials for all 1 ≤ i ≤ `. By using a method similar to that we used in the proof of Theorem 2.4, one can obtain the next theorem which gives the minimal generating set of 1-generator two-dimensional GQC codes over R. Theorem 3.3. Let C be a 1-generator two-dimensional GQC code of length (m1,m2, . . . ,m`) over R which is generated by G′(x,y) = (G′1(x,y),G ′ 2(x,y), . . . ,G ′ `(x,y)), where mi is odd for all i with 1 ≤ i ≤ `. Then G′i(x,y) = ϕ0i(x) + (u+ 1)ϕ1i(x) + (ψ0i(x) + (u+ 1)ψ1i)y + (θ0i(x) + (u+ 1)θ1i(x)y 2), where ϕ0i(x), ϕ1i(x), ψ0i(x), ψ1i(x), θ0i(x) and θ1i(x) are polynomials in R[x] for all i with 1 ≤ i ≤ `. Furthermore, ϕ0i(x), ψ0i(x) and θ1i(x) are monic polynomials for all 1 ≤ i ≤ `. Assume that deg(ϕ0i(x)) ≥ deg(ϕ1i(x)), deg(ψ0i(x)) ≥ deg(ψ1i(x)) and that deg(θ0i(x)) ≥ deg(θ1i(x)). Suppose that polynomials ϕ0i(x) + (u + 1)ϕ1i(x), (ψ0i(x) + (u + 1)ψ1i)y, (θ0i(x) + (u + 1)θ1i(x))y 2 are not zero-divisor of Ri. Let h0i = (x mi − 1)/gcd(ϕ0i(x),xmi − 1), h0 = lcm(h01, . . . ,h0l), deg(h0) = r0, δ0,i = (x mi − 1)/gcd(h0ϕ1i(x),xmi − 1), δ0 = lcm(δ01, . . . ,δ0`) and deg(δ0) = t0. Let h1i = (x mi − 1)/gcd(ψ0i(x),xmi − 1), h1 = lcm(h11,h12, . . . ,h1`), deg(h1) = r1, δ1i = (x mi − 1)/gcd(h1ψ1i(x),xmi − 1), δ1 = lcm(δ11,δ12, . . . ,δ1`) and deg(δ1) = t1. Suppose that h2i = (x mi − 1)/gcd(θ0i(x),xmi − 1), h2 = lcm(h21, . . . ,h2`), deg(h2) = r2, δ2i = (x mi − 1)/gcd(h2θ1i(x),xmi − 1), δ2 = lcm(δ21,δ22, . . . ,δ2`) and deg(δ2) = t2. 67 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Then the minimal generating set of C is S1 ∪S2 ∪S3 ∪S4 ∪S5 ∪S6, where S1 = r0−1⋃ j=0 {xj(ϕ01(x) + (u + 1)ϕ11(x), . . . ,ϕ0`(x) + (u + 1)ϕ1`(x))}, S2 = r1−1⋃ j=0 {xj((ψ01(x) + (u + 1)ψ1i(x))y, . . . , (ψ0`(x) + (u + 1)ψ1`(x))y)}, S3 = r2−1⋃ j=0 {xj((θ01(x) + (u + 1)θ11(x))y2, . . . , (θ0`(x) + (u + 1)θ1`(x))y2)}, S4 = t0−1⋃ j=0 {xj((u + 1)h0ϕ11(x), . . . , (u + 1)h0ϕ1`(x))}, S5 = t1−1⋃ j=0 {xj((u + 1)h1ψ11(x)y, . . . , (u + 1)h1ψ1`(x)y)}, S6 = t2−1⋃ j=0 {xj((u + 1)h2θ11(x)y2, . . . , (u + 1)h2θ1`(x)y2)}. Thus | C |= 16r0+r1+r2 4t0+t1+t2 . According to Theorem 3.3, we have the following corollary. Corollary 3.4. If ` is a positive integer and ϕ1i(x) = xmi −1, ψ1i(x) = xmi −1 and θ1i(x) = xmi −1 are polynomials over R for all i with 1 ≤ i ≤ `, then C is a free two-dimensional GQC code of rank r0 +r1 +r2 over R and its minimal generating set is S1 ∪S2 ∪S3. Furthermore, C has 16r0+r1+r2 codewords. In the following theorem, we give a lower bound on the minimum distance of free 1-generator two- dimensional GQC codes over R. Its proof is exactly the same as the proof of Theorem 2.6, so we delete it. Theorem 3.5. Let C be a free 1-generator two-dimensional GQC code of length (m1,m2, . . . ,m`) over R as in Corollary 3.4. Let h0i = (x mi − 1)/ϕ0i(x), h0 = lcm{h01, . . . ,h0`}, h1i = (x mi − 1)/ψ0i(x), h1 = lcm{h11, . . . ,h1`}, h2i = (x mi − 1)/θ0i(x) and h2 = lcm{h21, . . . ,h2`}. Then (i) dmin(C) ≥ ∑ i/∈A d0i + ∑ i/∈B d1i + ∑ i/∈D d2i, where A,B,D ⊆ {1, 2, . . . ,`} are sets of maximum size for which lcm{h0i, i ∈ A} 6= h0, lcm{h1j,j ∈ B} 6= h1 and lcm{h2t, t ∈ D} 6= h2. (ii) If h01 = h02 = . . . = h0`, h11 = h12 = . . . = h1` and h21 = h22 = . . . = h2`, then dmin(C) ≥ ∑̀ i=1 d0i + ∑̀ i=1 d1i + ∑̀ i=1 d2i. According to Corollary 3.4 and Theorem 3.5 we obtain the following corollary. 68 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 Corollary 3.6. Assume that ` is a positive integer and ϕ1i(x) = xmi − 1, ψ1i(x) = xmi − 1 and θ1i(x) = x mi − 1 are polynomials over R for all i with 1 ≤ i ≤ `. Let h0i = (x mi − 1)/ϕ0i(x), h0 = lcm{hoi, . . . ,h0`}, h1i = (x mi − 1)/ψ0i(x), h1 = lcm{h11, . . . ,h1`}, h2i = (x mi − 1)/θ0i(x) and h2 = lcm{h21, . . . ,h2`} for all 1 ≤ i ≤ `. Then we have the following statements. (i) C is a free two-dimensional code of rank deg(h0) + deg(h1) + deg(h2). Moreover, | C |= 16deg(h0)+deg(h1)+deg(h2), (ii) dmin(C) ≥ ∑ i/∈A d0i + ∑ j/∈B d1j + ∑ k/∈D d2k, where A, B, D ⊆{1, . . . ,`}, (iii) Let h01 = . . . = h0` = h0, h11 = . . . = h1` = h1 and h21 = . . . = h2` = h2. Then we have dmin(C) ≥ ∑` i=1 d0i + ∑` i=1 d1i + ∑` i=1 d2i. 4. Conclusion This paper is devoted to the study of two-dimensional quasi-cyclic codes and two-dimensional gen- eralized quasi-cyclic codes of length 3m` which are a natural generalization of quasi-cyclic codes and generalized quasi-cyclic codes over the ring R = Z4[u]/〈u2 − 1〉 with u2 = 1. We first determine the generator polynomials of two-dimensional cyclic codes over R. Then we find the generator polynomi- als of two-dimensional quasi-cyclic codes and two-dimensional generalized quasi-cyclic codes over R and give their minimal generating sets. Moreover, we study the minimum distances of the family of the free 1-generator two-dimensional quasi-cyclic codes and two-dimensional generalized quasi-cyclic codes. References [1] Y. Cao, Structural properties and enumeration of 1-generator generalized quasi-cyclic codes, Des. Codes Cryptogr. 60(1) (2011) 67–79. [2] Y. Cao, J. Gao, Constructing quasi-cyclic codes from linear algebra theory, Des. Codes Cryptogr. 67(1) (2013) 59–75. [3] M. Esmaeili, S. Yari, Generalized quasi-cyclic codes: structural properties and code construction, Appl. Algebra Engrg. Comm. Comput 20(2) (2009) 159–173. [4] Y. Gao, J. Gao, T. Wu, F. W. Fu, 1-generator quasi-cyclic and generalized quasi-cyclic codes over the ring Z4[u]〈u2−1〉, Appl. Algebra Engrg. Comm. Comput. 28(6) (2017) 457–467. [5] C. Güneri, F. Özbudak, B. Özkaya, E. SaÃğÄśkara, Z. Sepasdar, P. Solé, Structure and performance of generalized quasi-cyclic codes, Finite Fields Appl. 47 (2017) 183–202. [6] T. Ikai, H. Kosako, Y. Kojima, Two-dimensional cyclic codes, Electron. Comm. Japan 57(4) (1974/75) 27–35. [7] R. M. Lalasoa, R. Andriamifidisoa, T. J. Rabeherimanana, Basis of a multicyclic code as an ideal in Fq[X1, . . . ,Xs]/〈X ρ1 1 − 1, . . . ,X ρs s − 1〉, J. Algebra Relat. Topics 6(2) (2018) 63–78. [8] S. Ling, Ch. Xing, Coding theory: A first course, Cambridge University Press, New York (2004). [9] S. Ling, P. Solé, On the algebraic structure of quasi-cyclic codes. I. finite fields, IEEE Trans. Inform. Theory 47(7) (2001) 2751–2760. [10] M. Özen, F. Z. Uzekmek, N. Aydin, N.T. Özzaim, Cyclic and some constacyclic codes over the ring Z4[u] 〈u2−1〉, Finite Fields Appl. 38 (2016) 27–39. 69 https://doi.org/10.1007/s10623-010-9417-5 https://doi.org/10.1007/s10623-010-9417-5 https://doi.org/10.1007/s10623-011-9586-x https://doi.org/10.1007/s10623-011-9586-x https://doi.org/10.1007/s00200-009-0095-3 https://doi.org/10.1007/s00200-009-0095-3 https://doi.org/10.1007/s00200-017-0315-1 https://doi.org/10.1007/s00200-017-0315-1 https://doi.org/10.1016/j.ffa.2017.06.005 https://doi.org/10.1016/j.ffa.2017.06.005 https://mathscinet.ams.org/mathscinet-getitem?mr=456921 https://mathscinet.ams.org/mathscinet-getitem?mr=456921 https://mathscinet.ams.org/mathscinet-getitem?mr=3938616 https://mathscinet.ams.org/mathscinet-getitem?mr=3938616 https://doi.org/10.1017/CBO9780511755279 https://doi.org/10.1109/18.959257 https://doi.org/10.1109/18.959257 https://doi.org/10.1016/j.ffa.2015.12.003 https://doi.org/10.1016/j.ffa.2015.12.003 A. Ghajari et. al. / J. Algebra Comb. Discrete Appl. 9(1) (2022) 57–70 [11] Z. Sepasdar, Generator matrix for two-dimensional cyclic codes of arbitrary length, arXiv:1704.08070v1 [math.AC] 26 Apr (2017). [12] Z. Sepasdar, Some notes on the characterization of two dimensional skew cyclic codes, J. Algebra Relat. Topics 4(2) (2016) 1–8. [13] Z. Sepasdar, K. Khashyarmanesh, Characterizations of some two-dimensional cyclic codes correspond to the ideals of F[x,y]/〈xs − 1,y2 k − 1〉, Finite Fields Appl. 41 (2016) 97–112. [14] I. Siap, T. Abualrub, B. Yildiz, One generator quasi-cyclic codes over F2 + uF2, J. Frankl. Inst. 349(1) (2012) 284–292. 70 https://arxiv.org/abs/1704.08070 https://arxiv.org/abs/1704.08070 https://mathscinet.ams.org/mathscinet-getitem?mr=3597268 https://mathscinet.ams.org/mathscinet-getitem?mr=3597268 https://doi.org/10.1016/j.ffa.2016.06.003 https://doi.org/10.1016/j.ffa.2016.06.003 https://doi.org/10.1016/j.jfranklin.2011.10.020 https://doi.org/10.1016/j.jfranklin.2011.10.020 Introduction Generator polynomials 1-generator two-dimensional GQC codes Conclusion References