Automorphisms Of The Unipotent Subgroup Of The Chevalley Group Over The Integral Ring

Let G be the Cheva]ley ?Dernazure group scheme of the adjoint form deterniined by a complex semi ?simple Lie algebra ?and its adjoint representation ([9] ,[iO]), G(Z) be the Chevalley group over the integral ring Z.Let E(Z) denote the elementary matrix of G(Z), U the unipotent subgroup of E(Z). The aim of this paper is to determine the automorphisms of U. The main result of this paper is that any automorphism of U (except U is of type A1,A2, B2) can be expressed as a product of graph, diagonal, inner, extremal, and central automorphisms g, d, i, e, and c , of U.