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# Existence of anti-periodic solutions for second-order ordinary differential equations involving the Fučík spectrum

Xin Zhao1 and Xiaojun Chang2*

Author Affiliations

1 College of Information Technology, Jilin Agricultural University, Changchun, 130118, P.R. China

2 College of Mathematics, Jilin University, Changchun, Jilin, 130012, China

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Boundary Value Problems 2012, 2012:149  doi:10.1186/1687-2770-2012-149

 Received: 20 July 2012 Accepted: 20 September 2012 Published: 21 December 2012

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### Abstract

In this paper, we study the existence of anti-periodic solutions for a second-order ordinary differential equation. Using the interaction of the nonlinearity with the Fučík spectrum related to the anti-periodic boundary conditions, we apply the Leray-Schauder degree theory and the Borsuk theorem to establish new results on the existence of anti-periodic solutions of second-order ordinary differential equations. Our nonlinearity may cross multiple consecutive branches of the Fučík spectrum curves, and recent results in the literature are complemented and generalized.

##### Keywords:
anti-periodic solutions; Fučík spectrum; Leray-Schauder degree theory; Borsuk theorem

### 1 Introduction and main results

In this paper, we study the existence of anti-periodic solutions for the following second-order ordinary differential equation:

(1.1)

where , , and T is a positive constant. A function is called an anti-periodic solution of (1.1) if satisfies (1.1) and for all . Note that to obtain anti-periodic solutions of (1.1), it suffices to find solutions of the following anti-periodic boundary value problem:

(1.2)

In what follows, we will consider problem (1.2) directly.

The problem of the existence of solutions of (1.1) under various boundary conditions has been widely investigated in the literature and many results have been obtained (see [1-13]). Usually, the asymptotic interaction of the ratio with the Fučík spectrum of under various boundary conditions was required as a nonresonance condition to obtain the solvability of equation (1.1). Recall that the Fučík spectrum of with an anti-periodic boundary condition is the set of real number pairs such that the problem

(1.3)

has nontrivial solutions, where , ; while the concept of Fučík spectrum was firstly introduced in the 1970s by Fučík [14] and Dancer [15] independently under the periodic boundary condition. Since the work of Fonda [6], some investigation has been devoted to the nonresonance condition of (1.1) by studying the asymptotic interaction of the ratio , where , with the spectrum of under different boundary conditions; for instance, see [10] for the periodic boundary condition, [16] for the two-point boundary condition. Note that

we can see that the conditions on the ratio are more general than those on the ratio . In fact, by using the asymptotic interaction of the ratio with the spectrum of , the ratio can cross multiple spectrum curves of . In this paper, we are interested in the nonresonance condition on the ratio for the solvability of (1.1) involving the Fučík spectrum of under the anti-periodic boundary condition.

Note that the study of anti-periodic solutions for nonlinear differential equations is closely related to the study of periodic solutions. In fact, since , is a T-periodic solution of (1.1) if is a -anti-periodic solution of (1.1). Many results on the periodic solutions of (1.1) have been worked out. For some recent work, one can see [2-5,8-10,17]. As special periodic solutions, the existence of anti-periodic solutions plays a key role in characterizing the behavior of nonlinear differential equations coming from some models in applied sciences. During the last thirty years, anti-periodic problems of nonlinear differential equations have been extensively studied since the pioneering work by Okochi [18]. For example, in [19], anti-periodic trigonometric polynomials are used to investigate the interpolation problems, and anti-periodic wavelets are studied in [20]. Also, some existence results of ordinary differential equations are presented in [17,21-24]. Anti-periodic boundary conditions for partial differential equations and abstract differential equations are considered in [25-32]. For recent developments involving the existence of anti-periodic solutions, one can also see [33-35] and the references therein.

Denote by Σ the Fuc̆ík spectrum of the operator under the anti-periodic boundary condition. Simple computation implies that , where

It is easily seen that the set Σ can be seen as a subset of the Fuc̆ík spectrum of under the corresponding Dirichlet boundary condition; one can see the definition of the set , , or Figure 1 in [12]. Without loss of generality, we assume that is an eigenfunction of (1.3) corresponding to such that and . Denote and . Then if , we obtain only a one-dimensional function , denoted by , corresponding to the point , and if , we obtain only a one-dimensional function , denoted by , corresponding to the point .

In this paper, together with the Leray-Schauder degree theory and the Borsuk theorem, we obtain new existence results of anti-periodic solutions of (1.1) when the nonlinearity is asymptotically linear in s at infinity and the ratio stays asymptotically at infinity in some rectangular domain between Fučík spectrum curves and .

Our main result is as follows.

Theorem 1.1Assume that, . If the following conditions:

(i) There exist positive constantsρ, , Msuch that

(1.4)

(ii) There exist connect subset, constantsand a point of the typesuch that

(1.5)

and

hold uniformly for all,

In particular, if , then problem (1.3) becomes the following linear eigenvalue problem:

(1.6)

Simple computation implies that the operator with the anti-periodic boundary condition has a sequence of eigenvalues , , and the corresponding eigenspace is two-dimensional.

Corollary 1.2Assume that, . If (1.4) holds and there exist constantsp, qandsuch that

holds uniformly for all, then (1.1) admits a-anti-periodic solution.

Remark It is well known that (1.1) has a -anti-periodic solution if

for some (see Theorem 3.1 in [22]), which implies that the ratio stays at infinity asymptotically below the first eigenvalue of (1.6). In this paper, this requirement on the ratio can be relaxed to (1.4), with some additional restrictions imposed on the ratio . In fact, the conditions relative to the ratios and as in Theorem 1.1 and Corollary 1.2 may lead to that the ratio oscillates and crosses multiple consecutive eigenvalues or branches of the Fučík spectrum curves of the operator . In what follows, we give an example to show this.

Denote for some positive integer . Define

where . Clearly,

for all , , which imply that

(1.7)

(1.8)

for all . It is obvious that (1.7) implies that the assumption (i) of Theorem 1.1 holds. Take , , , such that . Then (1.8) implies that the assumption (ii) of Theorem 1.1 holds. Thus, by Theorem 1.1 we can obtain a -anti-periodic solution of equation (1.1). Here the ratio stays at infinity in the rectangular domain between Fučík spectrum curves and , while the ratio can cross at infinity multiple Fučík spectrum curves .

This paper is organized as follows. In Section 2, some necessary preliminaries are presented. In Section 3, we give the proof of Theorem 1.1.

### 2 Preliminaries

Assume that . Define

For , we can write the Fourier series expansion as follows:

Define an operator by

Clearly,

which implies that

(2.1)

Furthermore, we obtain

Note that

using the Parseval equality , we get

which implies that the operator J is continuous. In view of the Arzela-Ascoli theorem, it is easy to see that J is completely continuous.

Denote by deg the Leray-Schauder degree. We need the following results.

Lemma 2.1 ([[36], p.58])

Let Ω be a bounded open region in a real Banach spaceX. Assume thatis completely continuous and. Then the equationhas a solution in Ω if.

Lemma 2.2 ([[36], Borsuk theorem, p.58])

Assume thatXis a real Banach space. Let Ω be a symmetric bounded open region with. Assume thatis completely continuous and odd with. Thenis odd.

### 3 Proof of Theorem 1.1

Proof of Theorem 1.1 Consider the following homotopy problem:

(3.1)

(3.2)

where , .

We first prove that the set of all possible solutions of problem (3.1)-(3.2) is bounded. Assume by contradiction that there exist a sequence of number and corresponding solutions of (3.1)-(3.2) such that

(3.3)

Set . Obviously, and satisfies

(3.4)

(3.5)

By (1.4), (3.3) and the fact that f is continuous, there exist , such that

In view of , together with the choice of , it follows that there exists such that, for all ,

It is easily seen that and are uniformly bounded and equicontinuous on . Then, using the Arzela-Ascoli theorem, there exist uniformly convergent subsequences on for and respectively, which are still denoted as and , such that

(3.6)

Clearly, . Since is a solution of (3.1)-(3.2), for each n, we get

which implies that there exists such that . Then

(3.7)

Owing to that the sequences and are uniformly bounded, there exist and such that, passing to subsequences if possible,

(3.8)

Multiplying both sides of (3.4) by and integrating from to t, we get

Taking a superior limit as , by (3.3) and (3.6)-(3.8), we obtain

By the assumption (ii) and the choice of λ, if , we have

Similarly, we obtain

Note that , the above inequalities can be rewritten as the following equivalent forms:

(3.9)

(3.10)

It is easy to see that . In fact, if not, in view of (3.7)-(3.10), we get , , , which is contrary to .

We claim that has only finite zero points on . In fact, if not, we may assume that there are infinitely many zero points of . Without loss of generality, we assume that there exists such that . Letting in (3.9)-(3.10) and taking , we can obtain that . Without loss of generality, we assume that . Since is continuous, there exist such that , . Then there exists such that, if , we have

(3.11)

Clearly, , . Take with such that . Integrating (3.4) from to ,

(3.12)

By (3.3), (3.11), we obtain

holds uniformly for . Thus, using (1.4), we get

which implies that

Then, together with (3.6), (3.8) and (3.12), we obtain

Now, we show that (3.9)-(3.10) has only a trivial anti-periodic solution. In fact, if not, we assume that (3.9)-(3.10) has a nontrivial anti-periodic solution . Without loss of generality, we assume . Firstly, we consider the case that . Assume that , satisfy the following equations respectively:

(3.13)

(3.14)

with

(3.15)

(3.16)

Take as the first zero point of on . Then by (3.13)-(3.16) it follows that

(3.17)

In fact, by (3.15)-(3.16) and the fact that , , are continuous differential, it is easy to see that there exists sufficiently small such that

If there is such that , then comparing (3.9) with (3.13), we can obtain that , which implies that if , we have . Then for . Similarly, we have , . Hence, (3.17) holds.

Similarly, if , satisfy

(3.18)

(3.19)

and

then we obtain

where is the first zero point on .

Since has finite zero points, (3.13), (3.14), (3.18), (3.19) can be transformed into the following equations respectively:

(3.20)

(3.21)

Then there exist such that

It is easy to get

Since is anti-periodic and , there exists such that

which implies that there exists a real number pair such that

(3.22)

On the other hand, in view of the assumption (ii), by the definition of Σ and , it follows that

which is contrary to (3.22).

If , then by the assumption (ii), we can obtain a contradiction using similar arguments.

In a word, we can see that there exists independent of μ such that

(3.23)

Set

Clearly, Ω is a bounded open set in . Note that, for , using the assumption on f, we obtain

which implies that .

Define by

Clearly, is completely continuous, and by (2.1) and (3.1) it follows that the fixed point of in is the anti-periodic solution of problem (1.1). Define the homotopy as follows:

In view of (3.23), it follows that

Hence,

Note that the operator is odd. By Lemma 2.2 it follows that . Thus,

Now, using Lemma 2.1, we can see that (1.2) has a solution and hence (1.1) has a -anti-periodic solution. The proof is complete. □

### Competing interests

The authors declare that they have no competing interests.

### Authors’ contributions

All authors read and approved the final manuscript.

### Acknowledgements

The authors sincerely thank Prof. Yong Li for his instructions and many invaluable suggestions. This work was supported financially by NSFC Grant (11101178), NSFJP Grant (201215184), and the 985 Program of Jilin University.

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