Abstract

The existence of the nontrivial periodic solutions for the nonautonomous first order delay differential equation $x'(t)=-[f(t, x(t-1))+f(t, x(t-2))+\cdots+f(t, x(t-(2N-1)))]$ is investigated, where $f\in C({\mathbf{R}}\times{\mathbf{R}}, {\mathbf{R}})$ is 2N-periodic in t and odd in x, N is a positive integer. We prove several new existence results by some recent critical point theorems.

Highlights

  • It is well known that critical point theory is a powerful tool that deals with the multiplicity of periodic solutions to ordinary differential systems as well as partial differential equations

  • We prove several new existence results by some recent critical point theorems

  • 1 Introduction It is well known that critical point theory is a powerful tool that deals with the multiplicity of periodic solutions to ordinary differential systems as well as partial differential equations

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Summary

Introduction

It is well known that critical point theory is a powerful tool that deals with the multiplicity of periodic solutions to ordinary differential systems as well as partial differential equations (see [ – ]). In the past several years, some results on the existence of periodic solutions for the functional differential equation were obtained by critical point theory (see [ – ]). Periodic solutions of the Hamiltonian systems are still obtained as critical points of a function φ over a Hilbert space E. The function φ is invariant and φ is equivariant about the compact group G This allows to find critical points of φ on a subspace of E which is invariant under the group G. We can apply Theorem A to obtain periodic solutions in this subspace, which surely have the required symmetric structure and give solutions to We denote by M+(·), M–(·) and M (·) the positive definite, negative definite, and null subspaces of the self-adjoint linear operator defining it, respectively

So we have
Since p

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