# Symmetric positive solutions of higher-order boundary value problems

Yan Luo

Author Affiliations

Department of Mathematics, Hunan University of Science and Technology, Xiangtan, Hunan, 411201, China

Boundary Value Problems 2014, 2014:78  doi:10.1186/1687-2770-2014-78

 Received: 31 October 2013 Accepted: 20 March 2014 Published: 3 April 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

We study the higher-order boundary value problems. The existence of symmetric positive solutions of the problem is discussed. Our results extend some recent work in the literature. The analysis of this paper mainly relies on the monotone iterative technique.

MSC: 34B15, 34B18.

##### Keywords:
higher-order boundary value problems; symmetric positive solutions; existence; monotone iterative technique

### 1 Introduction

We study the boundary value problem (BVP)

(1.1)

where is an integer, is continuous, , are nonnegative constants, , . may be singular at , (and/or ). If a function is continuous and satisfies for , then we say that is symmetric on . By a symmetric positive solution of BVP (1.1) we mean a symmetric function such that for and satisfies (1.1).

In recent years, many authors have studied BVP (1.1), they only considered that f is nondecreasing or nonincreasing in u, or the boundary condition depends only on derivatives of even orders; see [1-8] and references cited therein. To the best of the author’s knowledge, there is no such results involving (1.1). In this note, we intend to fill in such gaps in the literature.

The organization of this paper is as follows. After this introduction, in Section 2, we state the assumptions and some preliminary lemmas. By applying the monotone iterative technique, we discuss the existence of symmetric positive solutions for (1.1) and obtain the main results in Section 3.

### 2 Preliminaries

For convenience, in this paper we let , ,

(2.1)

(2.2)

where , and define

Remark 2.1 The set P is not a cone as it is not closed.

Throughout this paper, we assume the following:

(H1) , are nonnegative constants, , . is continuous and symmetric in t, i.e., f satisfies

(2.3)

(H2) For , is nondecreasing in u and there exists a constant such that if , then

(2.4)

(H2′) For , is nonincreasing in u and there exists a constant such that if , then

(2.5)

(H3) .

Example 2.1 Consider the equation

It is easy to see that the function f satisfies assumptions (H1) and (H2). In fact, if , there exists constant λ with such that .

Remark 2.2 It is easy to see that (H2) implies that if , then

(2.6)

and (H2′) implies that if , then

(2.7)

Now, we present several lemmas that will be used in the proof of our results. By routine calculations we have the following results.

Lemma 2.1Letvbe integrable on, then the BVP

has a unique solution

whereare defined by (2.1).

Lemma 2.2For any, we have

(2.8)

(2.9)

where, .

### 3 Main results

Define the operator by

(3.1)

where are defined by (2.1). It is clear that u is a solution of (1.1) if and only if u is a fixed point of T.

Theorem 3.1Assume (H1)-(H3) hold. Then BVP (1.1) has at least one symmetric positive solution.

Proof

Claim 3.1is completely continuous and nondecreasing.

In fact, for , it is obvious that , for and . (2.3), (2.9) and a change of variables imply

(3.2)

For any , from (2.4), (2.6), (2.8), and (H3), we have

(3.3)

(3.4)

for , where satisfies

Thus, it follows from (3.3) and (3.4) that , and so . Next by a standard method and the Ascoli-Arzela theorem one can prove that is completely continuous, we omit it here. From (H2), it is easy to see that T is nondecreasing in u. Hence, Claim 3.1 holds.

Claim 3.2Letbe fixed number satisfying

(3.5)

whereλis defined in (H2) in which, and assume

(3.6)

(3.7)

Then

(3.8)

and there existssuch that

(3.9)

In fact, since . So, from (3.5) and noting that , . From (3.6), we have and .

On the other hand, from (2.4) and (2.6), we have

Since and T is nondecreasing, by induction, (3.8) holds.

Let , then . It follows from

that, for any natural number n,

Thus, for all natural numbers n and p, we have

which implies that there exists such that (3.9) holds, and Claim 3.2 holds.

Letting in (3.7), we obtain , which is a symmetric positive solution of BVP (1.1), and this completes the proof of the theorem.  □

Theorem 3.2Assume (H1), (H2′) and (H3) hold. Then BVP (1.1) has at least one symmetric positive solution.

Proof

Claim 3.3is completely continuous and nonincreasing.

The proof of Claim 3.3 is similar to the proof of Claim 3.1, so this is omitted.

Claim 3.4Letbe fixed number, be sufficiently large constant satisfying

(3.10)

whereλis defined in (H2′) in which, and assume

(3.11)

Then

(3.12)

and there existssuch that

(3.13)

In fact, since and . So from (3.11),

(3.14)

From (2.5), (3.10), (3.14), and noting that T is nonincreasing in u, we have

(3.15)

(3.16)

Therefore,

(3.17)

(3.18)

From (3.15), (3.17), (3.18), and noting that is nondecreasing, by induction, (3.12) holds.

On the other hand, from (2.5) and (2.7), for ,

(3.19)

Then from (3.16) and (3.19), we have

and thus

Therefore, for all natural numbers n and p, we have

(3.20)

(3.21)

From (3.20) and (3.21), there exists such that (3.13) holds, and Claim 3.4 holds.

Letting in (3.11), we obtain , which is a symmetric positive solution of BVP (1.1), and this completes the proof of the theorem.  □

Remark 3.1[3,5] only considered that f is nondecreasing or nonincreasing in u, and , in (1.1), so our results extend the work in the literature.

Example 3.1 Consider the BVP

(3.22)

where for , , , .

It is easy to see that function satisfies (H1) and (H3). If , there exists constant λ with such that , so (H2) is also satisfied. Therefore, from Theorem 3.1, (3.22) has at least one symmetric positive solution.

### Competing interests

The author declares that she has no competing interests.

### Acknowledgements

Research supported by the Scientific Research Fund of Hunan Provincial Education Department (13C319).

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