On the membership of invertible diagonal matrices

Abstract

In this paper we consider decidability questions that are related to the membership problem in matrix semigroups. In particular we consider the membership of a particular invertible diagonal matrix in a matrix semigroup and then a scalar matrix, which has a separate geometric interpretation. Both problems have been open for any dimensions and are shown to be undecidable in dimenesion 4 with integral matrices and in dimension 3 with rational matrices by a reduction of the Post Correspondence Problem (PCP). Although the idea of PCP reduction is standard for such problems, we suggest a new coding technique to cover the case of diagonal matrices. © Springer-Verlag Berlin Heidelberg 2005.