Consider the linear system written in the matrical form
dz/dt = (A (t) + B(t)) z, z(to) = z,where A (t) and B (t) are n x n matrices and z an n X 1 matrix. It is well known that the solution takes the form z = u (t) v (t) z0,We may demand that both U (to) and V (to) are the identity matrix. The purpose of this paper is to establish the above type of decomposition formula for nonlinear cases and to study its application.Differential equations in this paper will be written in the form
Du= A (t)uwhere Du is the tangent vector to the solution path u(t) on a manifold ~ and A (t)u denotes the vector of the time-dependent vector field A (t) at the point u(t). The solution of (0.1) with the initial condition u(to)= Po will be written as u = T(A;t, to)Po. If a system of local coordinates x is chosen, then (0.1) takes the usual form du/dt = F (u, t), where both u and F are vectors. After some preparatory work in § 1, we define in § 2 the operation Adj a on vector fields, a being a homeomorphism from one open set to another of ~.
(A + B;t, to)Po= T (A;t, to) T(B*;t, to)po,where B* (t) = Adj T (A ; to, t) B (t). We also assert more or less to the effect that, for any vector field X on ~, if Y (t) = Adj T (A; t, to)X, then
r (t)/dt = [ Y (t), A (t)],where the right hand side is the usual bracket product of two infinitesimal transformations (vector fields).