On the equivalence of linear cyclic and constacyclic codes

TL;DR

This paper establishes new algebraic conditions for the equivalence of cyclic and constacyclic codes over finite fields, aiding in the classification and discovery of optimal codes.

Contribution

It provides novel criteria for code equivalence, including conditions for monomial and permutation equivalence, and simplifies the search for new codes over finite fields.

Findings

Monomial and isometric equivalence are identical for linear codes over finite fields.

A necessary and sufficient condition for monomial equivalence via shift maps is presented.

Conditions under which all permutation equivalent constacyclic codes are generated by multipliers.

Abstract

We introduce new sufficient conditions for permutation and monomial equivalence of linear cyclic codes over various finite fields. We recall that monomial equivalence and isometric equivalence are the same relation for linear codes over finite fields. A necessary and sufficient condition for the monomial equivalence of linear cyclic codes through a shift map on their defining set is also given. Moreover, we provide new algebraic criteria for the monomial equivalence of constacyclic codes over $\mathbb{F}_4$. Finally, we prove that if $\gcd(3n,\phi(3n))=1$, then all permutation equivalent constacyclic codes of length $n$ over $\mathbb{F}_4$ are given by the action of multipliers. The results of this work allow us to prune the search algorithm for new linear codes and discover record-breaking linear and quantum codes.