Butson full propelinear codes

Abstract

In this paper we study Butson Hadamard matrices, and codes over finite rings coming from these matrices in logarithmic form, called BH-codes. We introduce a new morphism of Butson Hadamard matrices through a generalized Gray map on the matrices in logarithmic form, which is comparable to the morphism given in a recent note of Ó Catháin and Swartz. That is, we show how, if given a Butson Hadamard matrix over the k{mathrm{th}} roots of unity, we can construct a larger Butson matrix over the ell mathrm{th} roots of unity for any ell dividing k, provided that any prime p dividing k also divides ell . We prove that a {mathbb {Z}}_{p^s}-additive code with p a prime number is isomorphic as a group to a BH-code over {mathbb {Z}}_{p^s} and the image of this BH-code under the Gray map is a BH-code over {mathbb {Z}}_p (binary Hadamard code for p=2). Further, we investigate the inherent propelinear structure of these codes (and their images) when the Butson matrix is cocyclic. Some structural properties of these codes are studied and examples are provided.