Some problems of the linear theory of systems of ordinary differential equations

We consider problems of the linear theory of systems of ordinary differential equations related to the investigation of invariant hyperplanes of these systems, the notion of equivalence for these systems, and the Floquet–Lyapunov theory for periodic systems of linear equations. In particular, we introduce the notion of equivalence of systems of linear differential equations of different orders, propose a new formula of the Floquet form for periodic systems, and present the application of this formula to the introduction of amplitude–phase coordinates in a neighborhood of a periodic trajectory of a dynamical system.     

On conjugacy of high-order linear ordinary differential equations

It is shown that the differential equation

On comparison systems for ordinary differential equations

We state and prove general comparison principles for ordinary differential equations, discuss the scope of these principles, and present examples.     

To the theory of degenerate systems of ordinary differential equations

Translated fromSibirskii Matemaiicheskii Zhurnal, Vol. 36, No. 5, pp. 1194–1207, September–October, 1995.     

On then-th order iterative ordinary linear differential equations

Summary It is shown that a change of the basis in the solution space of a second order linear differential equation induces a covariant change in the solution space of the corresponding iterative equation. Also studied is the problem to what extent a solution of an iterative equation determines the equation.Dedicated to the memory of Alexander M. Ostrowski on the occasion of the 100th anniversary of his birth.     

Exponential separation,exponential dichotomy and spectral theory for linear systems of ordinary differential equations

This paper is concerned with linear nonautonomous systems of ordinary differential equations. A criterion for exponential separation in terms of exponential dichotomy is given. As corollaries we obtain the roughness theorem for exponential separation and the new result that an upper triangular system on a half-line is exponentially separated if and only if the system corresponding to its diagonal is. A minimal decomposition into exponentially separated subspaces is defined. It turns out that it is, in general, finer than the Sacker-Sell spectral decomposition but that the two decompositions coincide for almost periodic systems.     

On extending existence theory from scalar ordinary differential equations to infinite quasimonotone systems of functional equations

In this paper we use Tarski's fixed point theorem to extend in a systematic way the existence of extremal solutions from scalar initial value problems to boundary value problems for infinite quasimonotone functional systems of differential equations.

     

Quasiperiodic solutions of degenerate linear systems of second-order ordinary differential equations

We establish sufficient conditions for the existence of quasiperiodic solutions of a system of ordinary second-order differential equations with degenerate symmetric matrix of the second derivatives for an arbitrary quasiperiodic inhomogeneity.     

A nonlocal problem for singular linear systems of ordinary differential equations

A system of linear ordinary differential equations is examined on an infinite half-interval. This system is supplemented by the boundedness condition for solutions and a nonlocal linear condition specified by the Stieltjes integral. A method for approximating the resulting problem by a problem posed on a finite interval is proposed, and the properties of the latter are investigated. A numerically stable method for solving this problem is examined. This method uses an auxiliary boundary value problem with separated boundary conditions.     

On periodic solutions of linear degenerate second-order ordinary differential equations

We consider a scalar linear second-order ordinary differential equation whose coefficient of the second derivative may change its sign when vanishing. For this equation, we obtain sufficient conditions for the existence of a periodic solution in the case of arbitrary periodic inhomogeneity.     

On uniqueness criteria for systems of ordinary differential equations

We present some new uniqueness criteria for the Cauchy problem

     

On the group classification of systems of two linear second-order ordinary differential equations with constant coefficients

The completeness of the group classification of systems of two linear second-order ordinary differential equations with constant coefficients is delineated in the paper. The new cases extend what has been done in the literature. These cases correspond to the type of equations where the commutative property of the coefficient matrices with respect to the dependent variables and the first-order derivatives in the considered system does not hold. A discussion of the results as well as a note on the extension to linear systems of second-order ordinary differential equations with more than two equations are given.     

On two comparison tests for linear second-order ordinary differential equations

We prove two comparison tests for second-order linear differential equations. The well-known Sturm comparison theorem is a straightforward corollary of the first of them. The second (integral) test permits one to use specific integral relations between the coefficients of two equations to prove the oscillation of one of the equations assuming the oscillation of the other.