The period and base of a reducible sign pattern matrix

A square sign pattern matrix AA (whose entries are +,-or0) is said to be powerful if all the powers A,A2,A3,…,A,A2,A3,…, are unambiguously defined. For a powerful pattern AA, if Al=Al+pAl=Al+p with ll and pp minimal, then ll is called the base of AA and pp is called the period of Li et al. [On the period and base of a sign pattern matrix, Linear Algebra Appl. 212/213 (1994) 101–120] characterized irreducible powerful sign pattern matrices. In this paper, we characterize reducible, powerful sign pattern matrices and give some new results on the period and base of a powerful sign pattern matrix.