On matrix-product structure of repeated-root constacyclic codes over finite fields

Abstract

For any prime number p, positive integers m,k,n, where n satisfies gcd(p,n)=1, and for any non-zero element λ0 of the finite field Fpm of cardinality pm, we prove that any λ0pk-constacyclic code of length pkn over the finite field Fpm is monomially equivalent to a matrix-product code of a nested sequence of pkλ0-constacyclic codes with length n over Fpm. As an application, we completely determine the Hamming distances of all negacyclic codes of length 7⋅2l over F7 for any integer l≥3.