Topological generators of abelian Lie groups and hypercyclic finitely   generated abelian semigroups of matrices
  In this paper we bring together results about the density of subsemigroups of abelian Lie groups, the minimal number of topological generators of abelian Lie groups and a result about actions of algebraic groups. We find the minimal number of generators of a finitely generated abelian semigroup or group of matrices with a dense or a somewhere dense orbit by computing the minimal number of generators of a dense subsemigroup (or subgroup) of the connected component of the identity of its Zariski closure. 
Herbert Abels and Antonios Manoussos
math.FA