# Sign-changing solution for a third-order boundary-value problem in ordered Banach space with lattice structure

Xiuli Lin* and Zengqin Zhao

Author Affiliations

School of Mathematical Sciences, Qufu Normal University, Qufu, 273165, P.R. China

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Boundary Value Problems 2014, 2014:132  doi:10.1186/1687-2770-2014-132

 Received: 11 December 2013 Accepted: 7 April 2014 Published: 22 May 2014

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 credited.

### Abstract

In this paper, the sign-changing solution of a third-order two-point boundary-value problem is considered. By calculating the eigenvalues and the algebraic multiplicity of the linear problem and using a new fixed point theorem in an ordered Banach space with lattice structure, we give some conditions to guarantee the existence for a sign-changing solution.

##### Keywords:
third-order boundary-value problem; sign-changing solution; Green’s function; fixed point; lattice

### 1 Introduction

In this paper, we consider the following nonlinear third-order two-point boundary-value problem

(1.1)

where .

The study on the existence of the sign-changing solutions for the boundary-value problem is very useful and interesting both in theory and in application. Recently, there has been much attention focused on the problem, especially to the two-point or multi-point boundary-value problem. For the second-order two-point or multi-point boundary-value problem, many beautiful results have been given on the existence and multiplicity of the sign-changing solutions (see [1-5] and the references therein). For example, Xu and Sun [1] obtained an existence result of the sign-changing solutions for the second-order three-point boundary-value problem

where , , . Xu [2] considered the sign-changing solutions for the second-order multi-point boundary-value problem

where , , , . In [4], Zhang and Sun obtained the existence and multiplicity of the sign-changing solutions for the integral boundary-value problem

(1.2)

where , is nonnegative with . For the integral boundary-value problem (1.2), Li and Liu [5] also obtained the existence and multiplicity of the sign-changing solutions in ordered Banach space with the lattice structure.

For the third-order boundary-value problem, the existence and multiplicity of solutions have also been discussed in many papers (see [6-11] and the references therein). However, the research on the sign-changing solutions has been proceeded slowly. For the problem (1.1), Yao and Feng [10,11] established several existence results for the solutions including the positive solutions using the lower and upper solutions and a maximum principle, respectively. To our knowledge, however, there are fewer papers considered the sign-changing solutions of the problem (1.1). Motivated by the work mentioned above, using the eigenvalues of linear operator, we give an existence result for the sign-changing solutions of the problem (1.1).

The main contribution of this paper are as follows: (a) for the sign-changing solutions of the problem (1.1), to our knowledge, there is no result using the eigenvalues of the linear operator until now; (b) we obtain the eigenvalues and the algebraic multiplicity of the linear problem corresponding the problem (1.1), which is one of the key points that we can use to prove our main result; (c) some conditions are given to guarantee the existence for a sign-changing solution of the problem (1.1).

### 2 Notations and preliminaries

The following results will be used throughout the paper.

Let , . Then E is a real Banach space with the norm . Let , and P is a normal solid cone of E, .

Let the operators K, F, A be defined by

(2.1)

and , respectively, where

(2.2)

Remark 1 (1) are completely continuous. (2) , . In fact, since it is obvious in the other case, we only need to prove the case . Now we suppose that . Then

Definition 2.1[12]

We call E a lattice under the partial ordering ≤, if and exist for arbitrary .

Remark 2 is a lattice under the partial ordering ≤ that is deduced by the cone of E.

Definition 2.2[12]

Let E be a Banach space with a cone be a nonlinear operator. We call that A is a unilaterally asymptotically linear operator along , if there exists a bounded linear operator L such that

L is said to be the derived operator of A along and will be denoted by . Similarly, we can also define a unilaterally asymptotically linear operator along . Specially, if , We call that A is a unilaterally asymptotically linear operator along P and −P.

Definition 2.3[12]

Let and be a nonlinear operator. A is said to be quasi-additive on lattice, if there exists such that

where , .

Remark 3 It is easy to see that the operators F and defined by (2.1) are both quasi-additive on the lattice .

Let us list some conditions and preliminary lemmas to be used in this paper.

(H1) is strictly increasing in u, and for all , .

(H2) uniformly on . There exists a positive integer such that

where are the positive solutions of the equation

(2.3)

(H3) uniformly on , and .

Lemma 2.1For any, is a solution of the following problem:

if and only ifis a solution of the integral equation

whereis defined by (2.2).

Proof On the one hand, integrating the equation

over for three times, we have

Then

Combining them with boundary condition , we conclude that

Therefore,

On the other hand, since

therefore,

and

Moreover, we get . □

Remark 4 Considering Lemma 2.1, we find that u is a solution of the problem (1.1) if and only if u is a fixed point of the operator .

From the following lemma, we can obtain the eigenvalues and the algebraic multiplicity of the linear operator K.

Lemma 2.2The eigenvalues of the linear operatorKare

and the algebraic multiplicity of each positive eigenvalueis equal to 1, whereare the positive solutions of (2.3).

Proof Let be a positive eigenvalue of the linear operator K, and be an eigenfunction corresponding to eigenvalue . By Lemma 2.1, we have

(2.4)

The auxiliary equation of the differential equation (2.4) has roots −μ, , , where . Thus the general solution of (2.4) is

Then

Applying the condition , we obtain , , where .

Applying the second condition , that is,

(2.5)

Considering (2.3), we see that μ is one of  , that is,

are eigenvalues of the linear operator K and the eigenfunction corresponding to the eigenvalue is

(2.6)

where C is a nonzero constant.

Next we prove that the algebraic multiplicity of the eigenvalue is 1. From (2.6), any two eigenfunctions corresponding to the same eigenvalue are merely nonzero constant multiples of each other, that is,

Now we show that

Obviously, we only need to show that

In fact, for any , is an eigenfunction of linear operator K corresponding to the eigenvalue if . Considering (2.6), there exists a nonzero constant σ such that

By direct computation, we have

(2.7)

It is easy to see that the solution for the corresponding homogeneous equation of (2.7) is of the form

Then, by an ordinary differential equation method, we see that the general solution of (2.7) is of the form

where

is the special solution of the equation

and

is the special solution of the equation

Then

Applying the condition , we obtain , . From the condition , we obtain

(2.8)

From (2.5), we have . Thus it follows from (2.8) that

which implies that

That is

Therefore, the algebraic multiplicity of the eigenvalue is 1. □

Lemma 2.3Suppose that (H1) holds andis a solution of the (1.1), then. Similarly, ifis a solution of the (1.1), then.

Proof The proof is obvious. □

Lemma 2.4Suppose that (H1)-(H3) hold. Then the operatorAis Fréchet differentiable atθand ∞, and, .

Proof Since (H3): uniformly on . That is, for any , there exists such that

From (H1), it is easy to see that , . Then, for any with , we have

Then

Thus,

which means .

Since (H2): uniformly on . That is, for any , there exists such that

Let . Then

Thus,

Then

Therefore, . □

Remark 5 Suppose (H2) holds. Similar to Lemma 2.4, we have

Lemma 2.5[13]

Suppose thatEis an ordered Banach space with a lattice structure, Pis a normal solid cone inE, and the nonlinear operatorAis quasi-additive on the lattice. Assume that

(i) Ais strongly increasing onPandP;

(ii) bothandexist withand; 1 is not an eigenvalue oforcorresponding a positive eigenvector;

(iii) ; the Fréchet derivativeofAatθis strongly positive, and;

(iv) the Fréchet derivativeofAatexists; 1 is not an eigenvalue of; the sumβof the algebraic multiplicities for all eigenvalues oflying in the intervalis an even number.

ThenAhas at least three nontrivial fixed points containing one sign-changing fixed point.

### 3 Main result

We state the main result of this paper.

Theorem 3.1Suppose that (H1)-(H3) hold. Then the problem (1.1) has at least three solutions including a sign-changing solution.

We need only to prove that satisfies the four conditions of Lemma 2.5.

Proof Noticing

(i) A is strongly increasing on P and −P. In fact, from (H1) and , we see that A is strongly increasing on P. Similarly, A is strongly increasing on −P.

(ii) From , and Lemma 2.2, we find that 1 is not an eigenvalue of or and .

(iii) From , , , Lemma 2.2 and (H1), we have is strongly positive, and .

(iv) Since , and Lemma 2.2, the condition (iv) of Lemma 2.5 is satisfied.

Therefore, from Lemma 2.5, we see that A has at least three nontrivial fixed points including one sign-changing fixed point. Then, the problem (1.1) has at least three solutions, including one sign-changing solution. □

Example 3.1 Consider the following third-order boundary-value problem

(3.1)

where

By simple calculations, we have , , , , . Then it is easy to see that satisfies the conditions (H1)-(H3). Therefore, the boundary-value problem (3.1) has at least three solutions, including one sign-changing solution.

### Competing interests

The authors declare that they have no competing interests.

### Authors’ contributions

The authors declare that the study was realized in collaboration with the same responsibility. All authors read and approved the final manuscript.

### Acknowledgements

The authors are highly grateful for the referees’ careful reading and comments on this paper. The research is supported by Program for Scientific research innovation team in Colleges and universities of Shandong Province, the Doctoral Program Foundation of Education Ministry of China (20133705110003), the Natural Science Foundation of Shandong Province of China (ZR2011AM008, ZR2012AM010, ZR2012AQ024).

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