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arXiv 1606.05019cs.ITmath.IT
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关于一类左亚循环码

On a class of left metacyclic codes

Cao Yonglin, Cao Yuan, Fu Fang-Wei, Gao Jian

摘要:

设$G_{(m,3,r)}=\langle x,y\mid x^m=1, y^3=1,yx=x^ry\rangle$是一个阶为$3m$的亚循环群,其中${\rm gcd}(m,r)=1$,$1<r<m$和$r^3\equiv 1$(mod $m$).则称群代数$\mathbb{F}_q[G_{(m,3,r)}]$的左理想为长度为$3m$的$\mathbb{F}_q$上的左亚循环码,简称为左$G_{(m,3,r)}$ -码.本文仅利用有限域理论和循环码、斜循环码的基本理论,针对${\rm gcd}(m,q)=1$和$r\equiv q^ε$的情形,对某个正整数$ε$建立了左$G_{(m,3,r)}$ -码的系统理论.证明了任意左$G_{(m,3,r)}$ -码都是由内码${\cal A}_i$和外码$C_i$组成的级联码的直和,其中${\cal A}_i$是$\mathbb{F}_q$上长度为$m$的最小循环码,$C_i$是$\mathbb{F}_q$的扩域上长度为$3$的斜循环码.然后给出了任意级联码中每个外码的显式表达式。给出了每个左$G_{(m,3,r)}$ -码的对偶码,确定了自正交左$G_{(m,3,r)}$ -码.

英文摘要:

Let $G_{(m,3,r)}=\langle x,y\mid x^m=1, y^3=1,yx=x^ry\rangle$ be a metacyclic group of order $3m$, where ${\rm gcd}(m,r)=1$, $1<r<m$ and $r^3\equiv 1$ (mod $m$). Then left ideals of the group algebra $\mathbb{F}_q[G_{(m,3,r)}]$ are called left metacyclic codes over $\mathbb{F}_q$ of length $3m$, and abbreviated as left $G_{(m,3,r)}$-codes. A system theory for left $G_{(m,3,r)}$-codes is developed for the case of ${\rm gcd}(m,q)=1$ and $r\equiv q^ε$ for some positive integer $ε$, only using finite field theory and basic theory of cyclic codes and skew cyclic codes. The fact that any left $G_{(m,3,r)}$-code is a direct sum of concatenated codes with inner codes ${\cal A}_i$ and outer codes $C_i$ is proved, where ${\cal A}_i$ is a minimal cyclic code over $\mathbb{F}_q$ of length $m$ and $C_i$ is a skew cyclic code of length $3$ over an extension field of $\mathbb{F}_q$. Then an explicit expression for each outer code in any concatenated code is provided. Moreover, the dual code of each left $G_{(m,3,r)}$-code is given and self-orthogonal left $G_{(m,3,r)}$-codes are determined.

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