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# Multiple solutions of three-point boundary value problems for second-order impulsive differential equation at resonance

Yulin Zhao1*, Haibo Chen2 and Qiming Zhang1

Author Affiliations

1 School of Science, Hunan University of Technology, Zhuzhou, Hunan, 412007, PR China

2 Department of Mathematics, Central South University, Changsha, Hunan, 410075, PR China

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Boundary Value Problems 2014, 2014:103  doi:10.1186/1687-2770-2014-103

 Received: 20 December 2013 Accepted: 8 April 2014 Published: 7 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, by using the coincidence degree theory and the upper and lower solutions method, we deal with the existence of multiple solutions to three-point boundary value problems for second-order differential equation with impulses at resonance. An example is given to show the validity of our results.

##### Keywords:
resonance; coincidence degree; upper and lower solutions; impulsive; three-point boundary value problems

### 1 Introduction

The purpose of the present paper is to investigate the following second-order impulsive differential equations:

(1.1)

together with the boundary conditions:

(1.2)

where , is a continuous differentiable function, is continuous, , for , m is a fixed positive integer, , , denotes the jump of at , . , (, ) represent the right limit (left limit) of and at , respectively.

Impulsive differential equations describe processes which experience a sudden change of their state at certain moments. The theory of impulse differential equations has been a significant development in recent years and played a very important role in modern applied mathematical models of real processes rising in phenomena studied in physics, population dynamics, chemical technology, biotechnology, and economics; see [1-10] and the references therein.

Recently, several authors (see [6,11-14] and the references therein) have studied the existence of nontrivial or positive solutions for second-order three-point boundary value problem of the type

(1.3)

Note that the nonlinear term f depends on u and its derivative , then the relative problem becomes more complicated. A general method to deal with this difficulty is to add some conditions to restrict the growth of the term. One condition is the Caratheodory nonlinearity, the other usual condition is Nagumo condition or Nagumo-Winter condition (see [2,9,12,15-20]). When , the linear operator is invertible, this is the so-called non-resonance case. Gupta et al. made use of the Leray-Schauder continuation theorem to get the results on the existence of the solution for the problems (1.3) when in [14]. By using the Leray-Schauder continuation theorem and in the presence of two pairs of upper and lower solutions, Khan and Webb [12] established the existence of at least three solutions for the problem (1.3) when . The linear operator is non-invertible when , this is the so-called resonance case, and the Leray-Schauder continuation theorem cannot be applied. In [11], by using the coincidence degree theory of Mawhin [21] and some linear or non-linear growth assumptions on f, Feng and Webb obtained the existence of the solution of the problem (1.3) when . By applying the nonlinear alternative of Leray-Schauder, Ma [13] have showed the existence of at least one solution for the problem (1.3) when .

Recently, using the coincidence degree theory and the concept of autonomous curvature bound set, Liu and Yu [6] have studied the existence of at least one solution for the problem (1.1)-(1.2) when , .

In the present paper, we assume that there exist n ( and ) pairs of upper and lower solutions for problem (1.1)-(1.2) and the nonlinear f satisfies a Nagumo-like growth condition with respect to . By considering a suitably modified nonlinearity and applying the coincidence degree method of Mawhin [21], the existence of multiple solutions for the problem (1.1)-(1.2) is given.

### 2 Preliminaries

Let

where

Obviously, X is a Banach space with the following norm:

In the following, we recall the concept of strict upper and lower solutions for problem (1.1)-(1.2).

Definition 2.1 A function is said to be a strict lower solution of the problem (1.1)-(1.2) if

(2.1)

(2.2)

(2.3)

Similarly, a function is said to be a strict upper solution of the problem (1.1)-(1.2) if

(2.4)

(2.5)

(2.6)

Remark 2.2 Let be continuous, , and is a solution of the problem (1.1)-(1.2), if is a strict lower solution (strict upper solution) for the problem (1.1)-(1.2) with (), then () on .

Definition 2.3 Let α be a strict lower solution and β be a strict upper solution for the problem (1.1)-(1.2) satisfying on J. We say that has property (H) relative to α and β, if there exists a function such that

(2.7)

for all , , and

(2.8)

where with , .

### 3 The key lemmas

Let , and

Then the problem (1.1)-(1.2) can be written as

Lemma 3.1Suppose thatLbe defined in the above. ThenLis a Fredholm operator of index zero. Furthermore

(3.1)

and

(3.2)

Proof Firstly, it is clear that (3.1) holds. Next, we shall prove that (3.2) holds.

The following problem:

(3.3)

has a solution satisfying and if and only if

(3.4)

In fact, if (3.3) has a solution satisfying , , then from (3.3) we have

According to , , we get (3.4).

On the other hand, if (3.4) holds, setting

where c is an arbitrary constant, then is a solution of (3.3) with , . Hence (3.2) holds. □

Take the projector as follows:

(3.5)

where , . For every , set

Thus, we obtain

Then . Hence . Since , we have , which implies . Hence L is a Fredholm operator of index zero.

Take , . So the generalized inverse of L can be written as

(3.6)

Set , . Then for the function ψ defined by (2.8), let be the solution of the following initial value problem:

(3.7)

and be the solution of the following initial value problem:

(3.8)

Lemma 3.2Suppose that there exists a constant, thenis well defined inand positive on this interval, is also well defined and positive in. Moreover, if, thenfor any; for any.

Proof We only consider the case (in the case , the proof is similar). Assume that there exists a such that . Let . It follows from (3.7) that

Integrating the above equation over we get (let )

However, the left side of the above equation equals ∞ by (2.8). We reach a contradiction. Hence for every . From , by the continuity of solution of differential equations on the initial values, we obtain for . The proof is complete. □

Define the following sets:

Define the function as

(3.9)

Lemma 3.3Let Deg denote the coincidence degree. Let the following conditions hold:

(i) , (Mis given in Lemma 3.2);

(ii) , , , ;

(iii) , and, .

Then

Proof Consider the following family of equations:

(3.10)

We will show

(3.11)

If not, then there exist some and such that (3.10) holds. Note that if and only if and either for some , or for some . There are two possibilities.

Case (I). If , , . In this case, , or .

Subcase (1). Suppose . Let . Then , and . When , , we get

If , then . From condition (i), we have

If , then for some and . Thus from (iii), we have

On the other hand, , and , thus

If , it is easy to see that . Since , we have , thus we can obtain . However, from condition (i) we know

If , then . This means that . Since , we have . However, according to the above arguments, we know , which is a contradiction.

Subcase (2). Suppose for , . Obviously, . Since . Thus we get

(3.12)

Let

Without loss of generality, we suppose that for . Then we have three possibilities.

(i) If , then there exists a sufficiently small neighborhood of such that . Thus , and has a local maximum value on , which implies . But in this case, from (3.7), (3.12), and (ii), we have

(3.13)

(ii) If , then there exists a sufficiently small neighborhood of such that . Thus , and has a local maximum value on , which implies . But in this case, from (3.8), (3.12), and (ii), we have

(iii) If , then there exists a sufficiently small neighborhood of such that . Thus . By the same argument as in (3.13), we reach a contradiction.

Case (II). for some . In this case, , or .

Subcase (3). Suppose for some . Let be defined in the above. Obviously, we have for and . It follows from (iii) that

If , then . Form (3.11) and (i), we have

If , together with (iii), we get . But and for , which yields , and we reach a contradiction.

Similar to subcase (2), we can show that is also impossible. Combining the results of case (I) and case (II) we obtain (3.11).

On the other hand, for , it follows from [21] that (3.10) is equivalent to the following family of operator equations:

(3.14)

where E is the identity mapping.

Note that , and

From (3.5) and (3.6), we have

and

By the Ascoli-Arzela theorem, it is easy to show that is bounded and is compact. Thus N is L-compact on .

Define a mapping ,

Then it is easy to prove that is completely continuous and we claim that

(3.15)

In fact, for , it follows from (3.10) and (3.14) that (3.15) holds. For , if there exists a such that , that is , in this case, , , hence or . However, it follows from (iii) that

Thus we get and , which contradicts for . Therefore (3.15) holds. As follows from [21] and by using the invariance of Leray-Schauder degree under homotopy, we obtain

Since KerL is one dimensional and , , we get

From the property of coincidence degree we proved Lemma 3.3. □

Lemma 3.4Assume that

(c1) there exist lower and upper solutions, of the problem (1.1)-(1.2), respectively, with;

(c2) is continuous and has property (H) relative toα, β;

(c3) , are continuous for each, and satisfy

Then.

Proof Choose large enough for , , , such that

and let () be defined in (3.7) and (3.8), then it follows from Lemma 3.2 that we can choose large enough such that

Define a set as

where is given in (3.9).

Define the auxiliary functions F and , as follows:

where

We then generalize F to and . It is easy to see that F, , are continuous and satisfy

Moreover, when , F, , are bounded. It follows from Lemma 3.3 that

where

Next we show

(3.16)

It suffices to show that

(3.17)

In fact, let such that and assume that

Case (1). If there exists , such that the function attains its maximum value , which implies and . But on the other hand,

(3.18)

which implies . We reach a contradiction.

If , then , . On the other hand, since and is a strict upper solution of problem (1.1)-(1.2), we see that . Thus . Note that assumes the maximum value at , there exists , such that and . By the same argument as in (3.18) where , we reach a contradiction.

If , then . According to (2.6), we get

if , which is a contradiction. Thus , which implies that also attains its maximum value at . By the same argument as in (3.18) where , we reach a contradiction.

Hence the function cannot have any nonnegative maximum value on the interval , for .

Case (2). If there exists a such that , from case (1), we get for some . Hence , , and consequently we have , which implies , because

Consequently, we get or and .

By the continuity of f and is a strict upper solution of problem (1.1)-(1.2), there exists a sequence with , , as such that

(3.19)

where are from the mean value theorem. As before, we also get

where . As a result, we can obtain

which is a contradiction to (3.19).

Case (3). If for all , then there must be a () such that , and , which implies . Namely, . However, this is impossible because

Thus we have proved that on J. Similarly we can show that on J. It then follows that on J.

We now shall prove that

(3.20)

Assume that (3.20) cannot hold. Thus there are two possibilities:

(a) There exists for some such that .

(b) There exists some such that .

For case (a), we assume .

Since . Thus we have

(3.21)

If , then there exists a sufficiently small neighborhood of τ such that . Thus and . However, it follows from (3.7) and (3.21) that

(3.22)

If , then there exists a sufficiently small neighborhood of τ such that . Thus and . However, it follows from (3.8) and (3.21) that

If , then there exists a sufficiently small neighborhood of τ such that . Thus and . By the similarly argument as in (3.22), we reach a contradiction.

Hence , , . Similarly, we can prove , , .

Likewise, we can show that case (b) is also impossible, and thus (3.20) holds. Combining the above results, we see that if , , then . Hence (3.17) is proved. From the property of coincidence, we know that (3.16) holds. Since in , , we have . The proof is complete. □

### 4 Main results

We are now in a position to prove our main result on the existence of at least solutions of boundary value problem (1.1)-(1.2).

Theorem 4.1Assume that

(H1) there existn (and) pairs of strict lower and upper solutions, of the problem (1.1)-(1.2) such that

(H2) , is continuous onand has property (H) relative to, ;

(H3) , are continuous for each, and satisfy

Then BVP (1.1)-(1.2) has at leastsolutionssuch that, and

Proof Choose large enough such that, for ,

and let be defined in (3.10), then it follows from Lemma 3.4 that we can take large enough such that, for all ,

Define the set () as

Also

For , we define the sets

Then by Lemma 3.4, we have

From the additive property of coincidence degree, we obtain

Since is arbitrary, we first deal with the case , the above discussion implies that the equation , that is, the problem (1.1)-(1.2) has at least one solution in the set , and respectively. That is, there exist at least three different solutions , and such that

and , .

For , replacing , , , by , , , respectively, then we can obtain another two different solutions , of the problem (1.1)-(1.2) such that

Along this way, we can complete the proof by the induction method. □

We now present an example to illustrate that the assumptions of our theorem can be verified.

Example 1 Consider the following boundary value problem:

(4.1)

where , , , , , .

First, we have and , thus , .

Next, it is clear that and are n ( and ) pairs of strict lower and upper solutions of the problem (4.1), respectively. It can be seen that , , , . Thus conditions (H1) and (H3) of Theorem (4.1) hold.

Since , it follows that

For all , we have

Take , then

Hence f has property (H). It follows from Theorem 4.1 that the problem (4.1) has at least different solutions such that

### 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 to the referees for careful reading and comments on this paper. The research is supported by Hunan Provincial Natural Science Foundation of China (No. 13JJ3106, and 12JJ2004); it is also supported by the National Natural Science Foundation of China (No. 61074067, 11271372, and 11201138).

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