# Mixed Monotone Iterative Technique for Impulsive Periodic Boundary Value Problems in Banach Spaces

- Pengyu Chen
^{1}Email author

**2011**:421261

**DOI: **10.1155/2011/421261

© Pengyu Chen. 2011

**Received: **20 April 2010

**Accepted: **15 September 2010

**Published: **21 September 2010

## Abstract

This paper deals with the existence of -quasi-solutions for impulsive periodic boundary value problems in an ordered Banach space . Under a new concept of upper and lower solutions, a new monotone iterative technique on periodic boundary value problems of impulsive differential equations has been established. Our result improves and extends some relevant results in abstract differential equations.

## 1. Introduction

The theory of impulsive differential equations is a new and important branch of differential equation theory, which has an extensive physical, chemical, biological, and engineering background and realistic mathematical model, and hence has been emerging as an important area of investigation in the last few decades; see [1]. Correspondingly, applications of the theory of impulsive differential equations to different areas were considered by many authors, and some basic results on impulsive differential equations have been obtained; see [2–5]. But many of them are about impulsive initial value problem; see [2, 3] and the references therein. The research on impulsive periodic boundary value problems is seldom; see [4, 5].

where , , ; ; is an impulsive function, . denotes the jump of at that is, where and represent the right and left limits of at , respectively.

But all of these results are in real spaces We not only consider problems in Banach spaces, but also expand the nonlinear term to the case of If is nondecreasing in and is nonincreasing in then the monotonity condition (1.3) is not satisfied, and the results in [4, 5] are not right, in this case, we studied the IPBVP(1.1). As far as we know, no work has been done for the existence of solutions for IPBVP(1.1) in Banach spaces.

Lakshmikantham et al. [6] and Guo and Lakshmikantham [7] obtained the existence of coupled quasisolutions of problem (1.5) by mixed monotone sequence of coupled quasiupper and lower solutions under the concept of quasiupper and lower solutions. In this paper, we improve and extend the above-mentioned results, and obtain the existence of the coupled minimal and maximal -quasisolutions and the solutions between the coupled minimal and maximal -quasisolutions of the problem (1.1) through the mixed monotone iterative about the coupled -quasisolutions. If the coupled upper and lower -quasisolutions are equivalent to coupled upper and lower quasisolutions of the IPBVP(1.1). If , and the coupled upper and lower -quasisolutions are equivalent to upper and lower solutions of IPBVP(1.4).

## 2. Preliminaries

Let be an ordered Banach space with the norm and partial order whose positive cone is normal with normal constant Let , is a constant; ; , , Let is continuous at , and left continuous at , and exists, Evidently, is a Banach space with the norm . An abstract function is called a solution of IPBVP(1.1) if satisfies all the equalities of (1.1)

Let and exist, . For it is easy to see that the left derivative of at exists and and set , then If is a solution of IPBVP(1.1), by the continuity of

Let denote the Banach space of all continuous -value functions on interval with the norm . Let denote the Kuratowski measure of noncompactness of the bounded set. For the details of the definition and properties of the measure of noncompactness, see [8]. For any and set If is bounded in then is bounded in and

Now, we first give the following lemmas in order to prove our main results.

Lemma 2.1 (see [9]).

Lemma 2.2 (see [10]).

Let be bounded. Then exist a countable set , such that

Lemma 2.3 (see [11]).

Lemma 2.4 (see [8]).

Let be a Banach space and is a bounded convex closed set in be condensing, then has a fixed point in

Lemma 2.5.

Proof.

where is a constant [3].

So, (2.4) is satisfied.

Inversely, we can verify directly that the function defined by (2.4) is a solution of the linear PBVP(2.3). Therefore, the conclusion of Lemma 2.5 holds.

Definition 2.6.

we call , coupled lower and upper -quasisolutions of the IPBVP(1.1). Only choose " " in (2.9) and (2.10), we call coupled -quasisolution pair of the IPBVP(1.1). Furthermore, if we call a solution of the IPBVP(1.1).

Evidently, is also an ordered Banach space with the partial order " " reduced by the positive cone . is also normal with the same normal constant . For with we use to denote the order interval in and to denote the order interval in .

## 3. Main Results

Theorem 3.1.

- (H1)
- (H2)
- (H3)
- (H4)

Then the IPBVP(1.1) has minimal and maximal coupled -quasisolutions between and which can be obtained by a monotone iterative procedure starting from and , respectively.

Proof.

By the definition of and Lemma 2.5, is continuous, and the coupled -quasisolutions of the IPBVP(1.1) is equivalent to the coupled fixed point of operator Combining this with the assumptions and , we know is a mixed monotone operator (about the mixed monotone operator, please see [6, 7]).

namely, . Similarly, it can be show that . So,

We prove that and are uniformly convergent in

For convenience, let , , , and . Since, and by (2.11) and the boundedness of and we easy see that and is equicontinuous in every interval so, is equicontinuous in every interval where , , From and it follows that and for Let , by Lemma 2.3, . Going from to interval by interval we show that in

Hence by the Belman inequality, in In particular, , this means that and are precompact in Thus and are precompact in and ,

Again by Belman inequality, in from which we obtain that , and ,

Continuing such a process interval by intervai up to we can prove that in every ,

Letting in (3.5) and (3.6), we see that and , By the mixed monotonicity of it is easy to see that and are the minimal and maximal coupled fixed points of in and therefore, they are the minimal and maximal coupled -quasisolutions of the IPBVP(1.1) in respectively.

In Theorem 3.1, if is weakly sequentially complete, condition and hold automatically. In fact, by Theorem in [12], any monotonic and order-bounded sequence is precompact. By the monotonicity (3.6) and the same method in proof of Theorem 3.1, we can easily see that and are convergent on In particular, and are convergent. So, condition holds. Let and be increasing or decreasing sequences obeying condition then by condition , is a monotonic and order-bounded sequence, so Hence, condition holds. From Theorem 3.1, we obtain the following corollary.

Corollary 3.2.

Let be an ordered and weakly sequentially complete Banach space, whose positive cone is normal, and , If the IPBVP(1.1) has coupled lower and upper -quasisolutions and with and conditions and are satisfied, then the IPBVP(1.1) has minimal and maximal coupled -quasisolutions between and which can be obtained by a monotone iterative procedure starting from and respectively.

We have the following result.

Theorem 3.3.

Let be an ordered Banach space, whose positive cone is normal, and , If the IPBVP(1.1) has coupled lower and upper -quasisolutions and with and conditions , , and hold, then the IPBVP(1.1) has minimal and maximal coupled -quasisolutions between and which can be obtained by a monotone iterative procedure starting from and respectively.

Proof.

where If is a increasing sequence and is a decreasing sequence, the above inequality is also valid. Hence holds.

Therefore, by Theorem 3.1, the IPBVP(1.1) has minimal and maximal coupled -quasisolutions between and which can be obtained by a monotone iterative procedure starting from and , respectively.

Now, we discuss the existence of the solution to the IPBVP(1.1) between the minimal and maximal coupled -quasisolutions and If we replace the assumptions and by the following assumptions:

for any where and are countable sets in

We have the following existence result.

Theorem 3.4.

Let be an ordered Banach space, whose positive cone is normal, and , If the IPBVP(1.1) has coupled lower and upper -quasisolutions and with such that assumptions , , and hold, then the IPBVP(1.1) has minimal and maximal coupled -quasisolutions and between and and at least has one solution between and

Proof.

Since is equicontinuous, by Lemma 2.3, . Combing (3.17) and .

Hence, the operator is condensing, by the Lemma 2.4, has fixed point in

Similarly, in general, letting we get Therefore, the IPBVP(1.1) at least has one solution between and

Remark 3.5.

If and then Theorems 3.1, 3.3 and 3.4 are generalizations of the main results of [5] in Banach spaces.

Remark 3.6.

If and then Theorems 3.1, 3.3 and 3.4 are generalizations of the Theory of [4] in Banach spaces.

## 4. An Example

### 4.1. Conclusion

IPBVP(4.1) has minimal and maximal coupled -quasisolutions.

Proof.

, Then it is easy to verify that , are coupled lower and upper -quasisolutions of the IPBVP(4.1), and conditions , hold. Hence, our conclusion follows from Corollary 3.2.

## Declarations

### Acknowledgments

This paper was supported by NNSF of China (10871160), the NSF of Gansu Province (0710RJZA103), and Project of NWNU-KJCXGC-3-47.

## Authors’ Affiliations

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