- Research Article
- Open Access

# The Existence of Positive Solution to a Nonlinear Fractional Differential Equation with Integral Boundary Conditions

- Meiqiang Feng
^{1}Email author, - Xiaofang Liu
^{1}and - Hanying Feng
^{2}

**2011**:546038

https://doi.org/10.1155/2011/546038

© Meiqiang Feng et al. 2011

**Received:**19 December 2010**Accepted:**26 January 2011**Published:**24 February 2011

## Abstract

The expression and properties of Green's function for a class of nonlinear fractional differential equations with integral boundary conditions are studied and employed to obtain some results on the existence of positive solutions by using fixed point theorem in cones. The proofs are based on the reduction of the problem considered to the equivalent Fredholm integral equation of the second kind. The results significantly extend and improve many known results even for integer-order cases.

## Keywords

- Fractional Derivative
- Fixed Point Theorem
- Fractional Differential Equation
- Real Banach Space
- Fixed Point Theory

## 1. Introduction

Fractional calculus is an area having a long history, its infancy dates back to three hundred years, the beginnings of classical calculus. It had attracted the interest of many old famous mathematicians, such as L'Hospital, Leibniz, Liouville, Riemann, Grünward, Letnikov, and so forth [1, 2]. As the old mathematicians expected, in recent several decades fractional differential equations have been found to be a powerful tool in more and more fields, such as materials, physics, mechanics, and engineering [1–5]. For the basic theory and recent development of the subject, we refer the reader to a text by Lakshmikantham et al. [6]. For more details and examples, see [7–24] and the references therein. However, the theory of boundary value problems for nonlinear fractional differential equations is still in the initial stages, and many aspects of this theory need to be explored.

where , is the standard Riemann-Liouville differentiation, and is a given continuous function.

where is a real number, and is the Caputo's fractional derivative. The function is continuous on .

, , are real numbers, and is a Banach space.

where , and may be singular at or/and at is the standard Riemann-Liouville differentiation, is nonnegative, and .

In the case of , for all , boundary value problem (1.5) reduces to the problem studied by Kaufmann and Mboumi [19]. In [19], the authors used the fixed point theorems to show sufficient conditions for the existence of at least one and at least three positive solutions to problem (1.5). For the case of , boundary value problem (1.5) is related to a boundary value problems of integer-order differential equation. Feng et al. [25] considered the existence and multiplicity of positive solutions to boundary value problem (1.5) by applying the fixed point theory in a cone for strict set contraction operators.

The organization of this paper is as follows. We will introduce some lemmas and notations in the rest of this section. In Section 2, we present the expression and properties of Green's function associated with boundary value problem (1.5). In Section 3, we give some preliminaries about operator. In particular, we state fixed point theory in cones. In Section 4, the main results of boundary value problem (1.5) will be stated and proved. In Section 5, we offer some interesting discussion of the associated boundary value problem (1.5). Finally, conclusions in Section 6 close the paper.

The fractional differential equations-related notations adopted in this paper can be found, if not explained specifically, in almost all literature related to fractional differential equations. The readers who are unfamiliar with this area can consult for example [1–6] for details.

Definition 1.1 (see [4]).

where is called Riemann-Liouville fractional integral of order .

Definition 1.2 (see [4]).

where , denotes the integer part of number , is called the Riemann-Liouville fractional derivative of order .

Lemma 1.3 (see [13]).

for some , , where is the smallest integer greater than or equal to .

## 2. Expression and Properties of Green's Function

In this section, we present the expression and properties of Green's function associated with boundary value problem (1.5).

Lemma 2.1.

Proof.

where is defined by (2.4).

where , , and are defined by (2.3), (2.4), and (2.5), respectively. The proof is complete.

From (2.3), (2.4), and (2.5), we can prove that , and have the following properties.

Proposition 2.2.

- (i)
is continuous for all , , for all ;

- (ii)
, for all , .

Proposition 2.3.

- (i)
is continuous for all , , for all ;

- (ii)
, for all , .

Proof.

From the properties of , and the definition of , we can prove that the results of Proposition 2.3 hold.

Theorem 2.4.

- (i)
is continuous for all , , for all ;

- (ii)

- (i)
From Propositions 2.2 and 2.3, we obtain that is continuous for all , , for all .

- (ii)

Remark 2.5.

where .

## 3. Preliminaries

In this section, we give some preliminaries for discussing the existence of positive solutions of boundary value problem (1.5).

where .

On the basis of Lemma 3.3 below we will establish in Section 4 the existence of positive solution to the problem (1.5). Here we make the following hypotheses:

(*H* _{
1
})
,
on any subinterval of (0,1) and
;

(*H* _{
2
})
and
uniformly with respect to
on
;

(*H* _{
3
})
, where
is defined by (2.21).

where is defined by (2.3).

Lemma 3.1.

Let (H_{1})–(H_{3}) hold. Then boundary value problems (1.5) has a solution
if and only if
is a fixed point of
.

Proof.

From Lemma 2.1, we can prove the results of this Lemma.

Lemma 3.2.

Let (H_{1})–(H_{3}) hold. Then
and
is completely continuous.

Proof.

For any , by (3.2), we can obtain . Next by similar proof of Lemma 3.1 in [12] and Ascoli-Arzela theorem one can prove is completely continuous. So it is omitted.

Lemma 3.3 (see [26]).

- (i)
There exists such that , for all , ; , for all , .

- (ii)
There exists such that , for all , ; , for all , .

Then, has at least one fixed point in .

## 4. Existence of Positive Solutions

In this section, we apply Lemma 3.3 to establish the existence of positive solutions for boundary value problems (1.5).

Theorem 4.1.

Suppose (H_{1})– (H_{3}) and
satisfies the following conditions.

(H_{4})There exists
such that
;

(H_{5})There exists
such that
.

Then boundary value problems (1.5) has at least one positive solution.

Proof.

Obviously, is a nonnegative continuous function, that is, , and .

*H*

_{ 4 }) and imply that there exist , such that

which is a contradiction to the definition of . Hence, (4.4) holds.

which is a contradiction to (4.9). So, (4.10) holds.

By (ii) of Lemma 3.3, (4.4) and (4.10) yield that has a fixed point , . Thus it follows that boundary value problems (1.5) has at least one positive solution with . The proof is complete.

## 5. Discussion

In this section, we offer some interesting discussion associated with boundary value problems (1.5).

- (i)
- (ii)
Obviously is continuous on , and it is easy to see that , by , where is defined by (2.21).

- (iii)

Obviously is continuous on , and it is easy to see that by , where is defined in (5.4).

## 6. Conclusions

In this paper, by using the fixed point theorem of cone, we have investigated the existence of positive solutions for a class of nonlinear fractional differential equations with integral boundary conditions and have obtained some easily verifiable sufficient criteria which extend previous results. It is worth mentioning that there are still many problems that remain open in this vital field other than the results obtained in this paper: for example, whether or not we can study the fractional differential equations with integral boundary conditions at resonance (see, e.g., [27]), and whether or not we can give a unified approach applicable to many BVPs (see, e.g., [28–31]). More efforts are still needed in the future.

## Declarations

### Acknowledgments

The authors thank the referee for his/her careful reading of the paper and useful suggestions. This paper is sponsored by the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the jurisdiction of Beijing Municipality (PHR201008430), the Scientific Research Common Program of Beijing Municipal Commission of Education (KM201010772018), the Natural Sciences Foundation of Heibei Province (A2009001426), and the Beijing Excellent Training Grant (2010D005007000002).

## Authors’ Affiliations

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