Maximum scattered linear sets and MRD-codes

Abstract

The rank of a scattered ${\mathbb{F}}_q$-linear set of $\mathrm{PG}(r-1,q^n)$, $rn$ even, is at most $rn/2$ as it was proved by Blokhuis and Lavrauw. Existence results and explicit constructions were given for infinitely many values of $r$, $n$, $q$ ($rn$ even) for scattered ${\mathbb{F}}_q$-linear sets of rank $rn/2$. In this paper we prove that the bound $rn/2$ is sharp also in the remaining open cases. Recently Sheekey proved that scattered ${\mathbb{F}}_q$-linear sets of $\mathrm{PG}(1,q^n)$ of maximum rank $n$ yield ${\mathbb{F}}_q$-linear MRD-codes with dimension $2n$ and minimum distance $n-1$. We generalize this result and show that scattered ${\mathbb{F}}_q$-linear sets of $\mathrm{PG}(r-1,q^n)$ of maximum rank $rn/2$ yield ${\mathbb{F}}_q$-linear MRD-codes with dimension $rn$ and minimum distance $n-1$.