Abstract
In this paper, we study the existence of antiperiodic solutions for a secondorder ordinary differential equation. Using the interaction of the nonlinearity with the Fučík spectrum related to the antiperiodic boundary conditions, we apply the LeraySchauder degree theory and the Borsuk theorem to establish new results on the existence of antiperiodic solutions of secondorder 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:
antiperiodic solutions; Fučík spectrum; LeraySchauder degree theory; Borsuk theorem1 Introduction and main results
In this paper, we study the existence of antiperiodic solutions for the following secondorder ordinary differential equation:
where , , and T is a positive constant. A function is called an antiperiodic solution of (1.1) if satisfies (1.1) and for all . Note that to obtain antiperiodic solutions of (1.1), it suffices to find solutions of the following antiperiodic boundary value problem:
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 [113]). 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 antiperiodic boundary condition is the set of real number pairs such that the problem
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 twopoint 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 antiperiodic boundary condition.
Note that the study of antiperiodic solutions for nonlinear differential equations is closely related to the study of periodic solutions. In fact, since , is a Tperiodic solution of (1.1) if is a antiperiodic solution of (1.1). Many results on the periodic solutions of (1.1) have been worked out. For some recent work, one can see [25,810,17]. As special periodic solutions, the existence of antiperiodic 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, antiperiodic problems of nonlinear differential equations have been extensively studied since the pioneering work by Okochi [18]. For example, in [19], antiperiodic trigonometric polynomials are used to investigate the interpolation problems, and antiperiodic wavelets are studied in [20]. Also, some existence results of ordinary differential equations are presented in [17,2124]. Antiperiodic boundary conditions for partial differential equations and abstract differential equations are considered in [2532]. For recent developments involving the existence of antiperiodic solutions, one can also see [3335] and the references therein.
Denote by Σ the Fuc̆ík spectrum of the operator under the antiperiodic 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 onedimensional function , denoted by , corresponding to the point , and if , we obtain only a onedimensional function , denoted by , corresponding to the point .
In this paper, together with the LeraySchauder degree theory and the Borsuk theorem, we obtain new existence results of antiperiodic 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
(ii) There exist connect subset, constantsand a point of the typesuch that
and
then (1.1) admits aantiperiodic solution.
In particular, if , then problem (1.3) becomes the following linear eigenvalue problem:
Simple computation implies that the operator with the antiperiodic boundary condition has a sequence of eigenvalues , , and the corresponding eigenspace is twodimensional.
Corollary 1.2Assume that, . If (1.4) holds and there exist constantsp, qandsuch that
holds uniformly for all, then (1.1) admits aantiperiodic solution.
Remark It is well known that (1.1) has a antiperiodic 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
In addition,
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 antiperiodic 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
For , we can write the Fourier series expansion as follows:
Clearly,
which implies that
Furthermore, we obtain
Note that
using the Parseval equality , we get
which implies that the operator J is continuous. In view of the ArzelaAscoli theorem, it is easy to see that J is completely continuous.
Denote by deg the LeraySchauder 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:
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
Set . Obviously, and satisfies
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 ArzelaAscoli theorem, there exist uniformly convergent subsequences on for and respectively, which are still denoted as and , such that
Clearly, . Since is a solution of (3.1)(3.2), for each n, we get
which implies that there exists such that . Then
Owing to that the sequences and are uniformly bounded, there exist and such that, passing to subsequences if possible,
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:
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
Clearly, , . Take with such that . Integrating (3.4) from to ,
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
a contradiction.
Now, we show that (3.9)(3.10) has only a trivial antiperiodic solution. In fact, if not, we assume that (3.9)(3.10) has a nontrivial antiperiodic solution . Without loss of generality, we assume . Firstly, we consider the case that . Assume that , satisfy the following equations respectively:
with
Take as the first zero point of on . Then by (3.13)(3.16) it follows that
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.
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:
It is easy to get
Since is antiperiodic and , there exists such that
which implies that there exists a real number pair such that
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
Set
Clearly, Ω is a bounded open set in . Note that, for , using the assumption on f, we obtain
Clearly, is completely continuous, and by (2.1) and (3.1) it follows that the fixed point of in is the antiperiodic 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 antiperiodic 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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