Automorphisms of direct products of finite groups II

In this paper we first find the automorphism group of the direct product of n copies of an indecomposable non-abelian group. We describe the automorphism group as matrices with entries which are homomorphisms between the n direct factors. We then use this description with a generalization of a result by Bidwell, Curran, and McCaughan on Aut (H × K), where H and K have no common direct factor, to provide structure and order theorems for an arbitrary direct product.