Periodic solutions for first order differential systems. (English) Zbl 1193.34084

Agarwal, Ravi P.; Chen, Jinhai

Appl. Math. Lett. 23, No. 3, 337-341 (2010).

The paper presents some existence and uniqueness results for periodic systems of the form
\[ {\mathbf x}' = G(t,{\mathbf x}), \qquad {\mathbf x} (0) = {\mathbf x} (2\pi), \]
where \(G(t,{\mathbf x}) : \mathbb{R} \times \mathbb{R}^n \to \mathbb{R}^n\) is Lipschitz continuous, \(2\pi\)-periodic in \(t\), and \(\frac{\partial G(t,{\mathbf x})}{\partial {\mathbf x}~~} \in \mathbb{R}^{n\times n}\) is continuous for \(t\in [0,2\pi], ~{\mathbf x} \in \mathbb{R}^n\).
The authors’ results are based on the spectral properties of the matrix function \(\frac{\partial G(t,{\mathbf x})}{\partial{\mathbf x}~~}\). An existence and uniqueness result is stated and proved.
Their method has applications to the case in which \(\frac{\partial G(t,{\mathbf x})}{\partial {\mathbf x}~~}\) is a block tridiagonal symmetric (or skew symmetric) Toeplitz matrix \(A(t)\), corresponding to the familiar linear vector system
\[ {\mathbf x}' = A(t){\mathbf x} + {\mathbf f} (t). \]
Two examples are given to illustrate their theory.
The novelty of their approach lies in their departure from other well established techniques in the literature such as fixed point theorems, continuation principles, and topological degree, often employed in the investigation of this and similar problems.

Reviewer: Awar Simon Ukpera (Ile-Ife)

MSC:

34C25	Periodic solutions to ordinary differential equations
34B15	Nonlinear boundary value problems for ordinary differential equations
34C15	Nonlinear oscillations and coupled oscillators for ordinary differential equations

Keywords:

first order differential systems; periodic solutions; initial value problems; fixed points.

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