On invariant manifolds of linear differential equations. II

Abstract: This is the continuation of previous article. For subspaces $M^n(t)$ and $M^{n-m}(t)$ which are invariant manifolds of the differential equation under consideration we build a change of variables which splits this equation into a system of two independent equations. A notion of equivalence of linear differential equations of different orders is introduced. Necessary and sufficient conditions of this equivalence are given. These results are applied to the Flocke-Lyapunov theory for linear equations with periodic coefficients with a period T. In the case when monodromy matrix of the equation has negative eigenvalues, thus reduction in $R^m$ to an equation with constant coeficcients is possible only with doubling of reduction matrix period, we prove the possibility of splitting off in $R^m$ of equations with negative eigenvalues of monodromy matrix with the help of a real matrix without period doubling. For the fundamental matrix of solutions of an equation with periodic coefficients $X(t), X(t)=E$, we find representation $X(t)=\Phi(t)e^{Ht}\Phi^{+}(0)$ with real rectangular matrices $H$ and $\Phi(t), \Phi(t)=\Phi(t+T)$. We bring two applications of these results: 1) reduction of nonlinear differential equation in $R^n$ with distinguished linear part which is periodic with period T to the equation in $R^m, m>n$, with a constiant matrix of coefficients of the linear part; 2) for introdusing of amplitude-phase coordinates in the neigbourhood of periodic orbit of autonomous differential equation with separation of the linear part with constant matrix of coefficients.