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Maximum rank‐distance (MRD) codes are (not necessarily linear) maximum codes in the rank‐distance metric space on m $m$‐by‐n $n$ matrices over a finite field Fq ${{\mathbb{F}}}_{q}$. They are diameter perfect and have the cardinality qm(n−d+1) ${q}^{m(n-d+1)}$ if m≥n $m\ge n$. We define switching in MRD codes as the replacement of special MRD subcodes by other subcodes with the same parameters. We consider constructions of MRD codes admitting switching, such as punctured twisted Gabidulin codes and direct‐product codes. Using switching, we construct a huge class of MRD codes whose cardinality grows doubly exponentially in m $m$ if the other parameters (n,q $n,\,q$, the code distance) are fixed. Moreover, we construct MRD codes with different affine ranks and aperiodic MRD codes. [ABSTRACT FROM AUTHOR]

We study codes with parameters of $q$ -ary shortened Hamming codes, i.e., $(n=(q^{m}-q)/(q-1), q^{n-m}, 3)_{q}$. Firstly, we prove the fact mentioned in 1998 by Brouwer et al. that such codes are optimal, generalizing it to a bound for multifold packings of radius-1 balls, with a corollary for multiple coverings. In particular, we show that the punctured Hamming code is an optimal $q$ -fold packing with minimum distance 2. Secondly, for every admissible length starting from $n=20$ , we show the existence of 4-ary codes with parameters of shortened 1-perfect codes that cannot be obtained by shortening a 1-perfect code. [ABSTRACT FROM AUTHOR]

In this paper, we give a new method to answer a recent conjecture proposed by Budaghyan, Calderini, Carlet, Davidova and Kaleyski about the equation x d + (x + 1) d = b in F q 4 , where n is a positive integer, q = 2 n and d = q 3 + q 2 + q − 1. In particular, we directly determine the differential spectrum of this power function x d using a more simple and direct method compared with those in the literature. [ABSTRACT FROM AUTHOR]

Cyclic codes have many applications in consumer electronics, communication and data storage systems due to their efficient encoding and decoding algorithms. An efficient approach to constructing cyclic codes is the sequence approach. In their articles (Ding and Zhou 2014 [11]) and (Ding, 2013 [7]), Ding and Zhou constructed several classes of cyclic codes from almost perfect nonlinear (APN) functions and planar functions over finite fields and presented some open problems on cyclic codes from highly nonlinear functions. This article focuses on these exciting works by investigating new insights in this research direction. Specifically, its objective is twofold. The first is to provide a complement with some former results and present correct proofs and statements on some known ones on the cyclic codes from the APN functions. The second is studying the cyclic codes from some known functions processing low differential uniformity. Along with this article, we shall answer some open problems presented in the literature. The first concerns Open Problem 1, proposed by Ding and Zhou (2014) [11]. The others are Open Problems 5.16 and 5.25, raised by Ding (2013) [7]. [ABSTRACT FROM AUTHOR]

We prove that the covering radius of the Melas code $M(m,q)$ of length $n=q^{m}-1$ over $\mathbb {F}_{q}$ is 2 if $q > 3$. We also prove that the covering radius of $M(m,3)$ is 3 is $m \ge 3$ , the covering radius of $M(2,3)$ is 4, and the covering radii of $M(1,2)$ and $M(1,3)$ are 1. [ABSTRACT FROM AUTHOR]

We construct strongly walk-regular graphs as coset graphs of the duals of codes with three non-zero homogeneous weights over Z p m , for p a prime, and more generally over chain rings of depth m, and with a residue field of size q, a prime power. In the case of p = m = 2 , strong necessary conditions (diophantine equations) on the weight distribution are derived, leading to a partial classification in modest length. Infinite families of examples are built from Kerdock and generalized Teichmüller codes. As a byproduct, we give an alternative proof that the Kerdock code is nonlinear. [ABSTRACT FROM AUTHOR]

It is well-known that cyclic codes have efficient encoding and decoding algorithms. In recent years, antiprimitive BCH codes have attracted a lot of attention. The objective of this paper is to study BCH codes of this type over finite fields and analyse their parameters. Some lower bounds on the minimum distance of antiprimitive BCH codes are given. The BCH codes presented in this paper have good parameters in general, containing many optimal linear codes. In particular, two open problems about the minimum distance of BCH codes of this type are partially solved in this paper. [ABSTRACT FROM AUTHOR]

The symbol-pair read channel was first proposed by Cassuto and Blaum. Later, Yaakobi et al. generalized it to the b -symbol read channel. It is motivated by the limitations of the reading process in high density data storage systems. One main task in b -symbol coding theory is to determine the b -symbol weight hierarchy of codes. In this paper, we study the b -symbol weight hierarchy of the Kasami codes, which are well known for their applications to construct sequences with optimal correlation magnitudes. The complete symbol-pair weight distribution of the Kasami codes is determined. [ABSTRACT FROM AUTHOR]

We investigate fat projective linear codes over ${\mathbb Z}_{p^{m}}$ , $m\geqslant 2$ , with two nonzero homogeneous weights (“two-weight codes”), building on the graph theory approach developed by Delsarte for codes over fields. Our main result is the classification of such codes under the additional assumption that the columns of a generator matrix of the code determine a cap in the projective Hjelmslev geometry $\mathop {\mathrm {PHG}}\nolimits (k-1, {\mathbb Z}_{p^{m}})$. This generalizes a result on projective two weight codes with dual distance at least four (Calderbank, 1982). The proof relies on a careful analysis of a certain strongly regular graph built on the cosets of the dual code, and on an interpretation of its parameters in terms of projective Hjelmslev geometry. [ABSTRACT FROM AUTHOR]

We study the codes of the title by the CRT method, that decomposes such codes into constituent codes, which are shorter codes over larger alphabets. Criteria on these constituent codes for self-duality and linear complementary duality of the decomposed codes are derived. The special class of the one-generator codes is given a polynomial representation and exactly enumerated. In particular, we present some illustrative examples of binary optimal linear codes with respect to the Griesmer bound derived from the $\mathbb {Z}_{2} \mathbb {Z}_{4}$ -additive quasi-cyclic codes. [ABSTRACT FROM AUTHOR]

A finite metric space is called here distance degree regular if its distance degree sequence is the same for every vertex. A notion of designs in such spaces is introduced that generalizes that of designs in Q-polynomial distance-regular graphs. An approximation of their cumulative distribution function, based on the notion of Christoffel function in approximation theory is given. As an application we derive limit laws on the weight distributions of binary orthogonal arrays of strength going to infinity. An analogous result for combinatorial designs of strength going to infinity is given. [ABSTRACT FROM AUTHOR]

We study the k-Galois linear complementary dual (LCD) codes over the finite chain ring R = Fq + uFq with u2 = 0, where q = pe and p is a prime number. We give a sufficient condition on the generator matrix for the existence of k-Galois LCD codes over R. Finally, we show that a linear code over R (for k = 0, q > 3) is equivalent to a Euclidean LCD code, and a linear code over R (for 0, (pe−k + 1) (pe−1) and (pe−1)/(pe−k + 1) > 1) is equivalent to a k-Galois LCD code. [ABSTRACT FROM AUTHOR]

If S is a transitive metric space, then | C | ⋅ | A | ≤ | S | for any distance- d code C and a set A , "anticode", of diameter less than d. For every Steiner S (t , k , n) system S , we show the existence of a q -ary constant-weight code C of length n , weight k (or n − k), and distance d = 2 k − t + 1 (respectively, d = n − t + 1) and an anticode A of diameter d − 1 such that the pair (C , A) attains the code–anticode bound and the supports of the codewords of C are the blocks of S (respectively, the complements of the blocks of S). We study the problem of estimating the minimum value of q for which such a code exists, and find that minimum for small values of t. [ABSTRACT FROM AUTHOR]

Modular strongly regular graphs have been introduced by Greaves et al. (Linear Algebra Appl 639:50–80, 2022). We show that a related class of isodual codes is asymptotically good. Equiangular tight frames over finite fields also introduced by the same authors in 2022 are shown here to connect with self-dual codes. We give several examples of equiangular tight frames over finite fields arising from self-dual codes. [ABSTRACT FROM AUTHOR]

In this paper, all of the conjectures in Aydin et al. (2022) [6] are settled: some proven correct, some proven correct with a modification, and some disproven, involving the equivalence and duality of polycyclic codes associated with trinomials. We also give methods to construct isodual and self-dual polycyclic codes, and study the self-orthogonal and dual-containing polycyclic codes over F 2. [ABSTRACT FROM AUTHOR]

In this paper, we introduce Toeplitz codes of index t , which are a generalization of quasi-cyclic codes of index t. We show that such codes meet the asymptotic Gilbert-Varshamov bound on the relative distance with asymptotic rate 1 t over F q , so they are asymptotically good for any t. We characterize some special classes of Toeplitz codes as LCD codes (resp. linear codes with one-dimensional hull or self-orthogonal codes). It is worth mentioning that we determine the hull dimension of the isometric image of a linear code. Some optimal or almost optimal binary linear codes are obtained as a result. Most importantly, we obtain some optimal or almost optimal LCD codes (resp. linear codes with one-dimensional hull) from quasi-cyclic codes. In particular, we construct binary LCD [ 32 , 16 , 8 ] , [ 33 , 11 , 11 ] and [ 34 , 17 , 8 ] codes with improved parameters directly. [ABSTRACT FROM AUTHOR]

We study codes with parameters of the ternary Hamming (n = (3 m − 1) / 2 , 3 n − m , 3) code, i.e., ternary 1-perfect codes. The rank of the code is defined to be the dimension of its affine span. We characterize ternary 1-perfect codes of rank n − m + 1 , count their number, and prove that all such codes can be obtained from each other by a sequence of two-coordinate switchings. We enumerate ternary 1-perfect codes of length 13 obtained by concatenation from codes of lengths 9 and 4; we find that there are 93241327 equivalence classes of such codes. [ABSTRACT FROM AUTHOR]

In the paper, we firstly study the algebraic structures of Z p Z p k -additive cyclic codes and give the generator polynomials and the minimal spanning set of these codes. Secondly, a necessary and sufficient condition for the Z p Z p 2 -additive cyclic code whose Gray image is linear (not necessarily cyclic) over Z p is given. Moreover, as for some special families of cyclic codes over Z p 2 and Z p Z p 2 , the linearity of the Gray images is determined. [ABSTRACT FROM AUTHOR]

We show that no more new distance-regular graphs in the tables of the book of (Brouwer, Cohen, Neumaier, 1989) can be produced by using the coset graph of additive completely regular codes over finite fields. [ABSTRACT FROM AUTHOR]

An additive cyclic code of length n over F 4 can be defined equivalently as an F 2 [ x ] / 〈 x n + 1 〉 -submodule of F 4 [ x ] / 〈 x n + 1 〉. In this paper we study additive cyclic and complementary dual codes of odd length over F 4 with respect to the trace Hermitian inner product and the trace Euclidean inner product. We characterize subfield subcodes and trace codes of these codes by their generators as binary cyclic codes. [ABSTRACT FROM AUTHOR]

In this paper, we construct new infinite families of codes over the ring R = F 2 + u F 2 + v F 2 + u v F 2 , u 2 = v 2 = 0 , u v = v u by employing simplicial complexes. When the simplicial complexes are all generated by a single maximal element, we compute the Lee weight distributions of these classes of codes. By the Gray map, we show that some classes of codes are minimal and some classes of these codes are distance optimal. [ABSTRACT FROM AUTHOR]

Double Toeplitz (DT) codes are codes with a generator matrix of the form (I , T) with T a Toeplitz matrix, that is to say constant on the diagonals parallel to the main. When T is tridiagonal and symmetric we determine its spectrum explicitly by using Dickson polynomials, and deduce from there conditions for the code to be LCD. Using a special concatenation process, we construct optimal or quasi-optimal examples of binary and ternary LCD codes from DT codes over extension fields. [ABSTRACT FROM AUTHOR]

Quasi-complementary sequence sets (QCSSs) play an important role in multi-carrier code-division multiple-access (MC-CDMA) systems. They can support more users than perfect complementary sequence sets in MC-CDMA systems. It is desirable to design QCSSs with good parameters that are a trade-off of large set size, small periodic maximum magnitude correlation and small alphabet size. The main results are to construct new infinite families of QCSSs that all have small alphabet size and asymptotically optimal periodic maximum magnitude correlation. In this paper, we propose three new constructions of QCSSs using additive characters over finite fields. Notably, these QCSSs have new parameters and small alphabet sizes. Using the properties of characters and character sums, we determine their maximum periodic correlation magnitudes and prove that these QCSSs are asymptotically optimal with respect to the lower bound. [ABSTRACT FROM AUTHOR]

Let q = p h be a prime power and e be an integer with 0 ≤ e ≤ h − 1. e -Galois self-orthogonal codes are generalizations of Euclidean self-orthogonal codes (e = 0) and Hermitian self-orthogonal codes (e = h 2 and h is even). In this paper, we propose two general methods to construct e -Galois self-orthogonal (extended) generalized Reed-Solomon (GRS) codes. As a consequence, eight new classes of e -Galois self-orthogonal (extended) GRS codes with odd q and 2 e | h are obtained. Based on the Galois dual of a code, we also study its punctured and shortened codes. As applications, new e ′ -Galois self-orthogonal maximum distance separable (MDS) codes for all possible e ′ satisfying 0 ≤ e ′ ≤ h − 1 , new e -Galois self-orthogonal MDS codes via the shortened codes, and new MDS codes with prescribed dimensional e -Galois hull via the punctured codes are derived. Moreover, some new q -ary quantum MDS codes with length greater than q + 1 and minimum distance greater than q 2 + 1 are obtained. [ABSTRACT FROM AUTHOR]