General Approach to Poset and Additive Metrics

Abstract

Let $P=([n],\leq _{P})$ be a poset on $[n] = \{1,2,\ldots,n\}$ , $\mathbb {F}_{q}^{n}$ be the linear space of $n$ -tuples over a finite field $\mathbb {F}_{q}$ and $w$ be a weight on $\mathbb {F}_{q}$ . In this paper we consider metrics on $\mathbb {F}_{q}^{n}$ which are induced by posets over $[n]$ and weights over $\mathbb {F}_{q}$ . Such family of metrics extend both the additive metric induced by the weight $w$ (when the poset is an anti-chain) and the poset metrics (when the weight is the Hamming weight). Furthermore, the pomset metrics is also a particular case of our construction, consequently, we provide a simpler approach to these metrics without using the multiset structure originally proposed. For the general case, we provide a complete description of the groups of linear isometries of these metric spaces in terms of a semi-direct product, which turns out to be similar to the case of poset metric spaces. In particular, we (re)obtain the groups of linear isometries of the poset, pomset and additive metric spaces. When considering a chain order, we develop, for codes on these spaces, several of the invariants and properties found in the classical coding theory. Our construction of metrics based on partial orders and any weight over the base field, highlights the dependence of the poset metric over $\mathbb {F}_{q}^{n}$ with the Hamming metric on $\mathbb {F}_{q}$ and the additive property of its extension on $\mathbb {F}_{q}^{n}$ .