Abstract and Applied Analysis

VolumeΒ 2012Β (2012), Article IDΒ 389530, 15 pages

http://dx.doi.org/10.1155/2012/389530

## Multiple Solutions for a Class of Multipoint Boundary Value Systems Driven by a One-Dimensional -Laplacian Operator

Department of Mathematics, Faculty of Sciences, Razi University, Kermanshash 67149, Iran

Received 20 November 2011; Accepted 11 December 2011

Academic Editor: KanishkaΒ Perera

Copyright Β© 2012 Shapour Heidarkhani. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

Employing a recent three critical points theorem due to Bonanno and Marano (2010), the existence of at least three solutions for the following multipoint boundary value system in , , for , is established.

#### 1. Introduction

In this work, we consider the following multipoint boundary value system for , where for , , , is a function such that is continuous in for all , is in for every and for all , for and , and denotes the partial derivative of with respect to for .

The study of multiplicity of solutions is an important mathematical subject which is also interesting from the practical point of view because the physical processes described by boundary value problems for differential equations exhibit, generally, more than one solution. In [1β3], Ricceri proposed and developed an innovative minimal method for the study of nonlinear eigenvalue problems. Following that, Bonanno [4] gave an application of the method to the two-point problem Bonanno also gave more precise versions of the three critical points of Ricceri in [5, 6]. In particular, in [5], an upper bound of the interval of parameters for which the functional has three critical points is established. Candito [7] extended the main result of [4] to the nonautonomous case In [8], He and Ge extended the main results of [4, 7] to the quasilinear differential equation In [9], the authors extended the main results of [4, 7, 9] to the quasilinear differential equation with Sturm-Liouville boundary conditions where is a constant, is a positive parameter, . In particular, in [10], the authors motivated by these works, established some criteria for the existence of three classical solutions of the system (1.1), while in [11], based on Ricceriβs three critical points theorem [3], the existence of at least three classical solutions to doubly eigenvalue multipoint boundary value systems was established.

In the present paper, based on a three critical points theorem due to Bonanno and Marano [12], we ensure the existence of least three classical solutions for the system (1.1).

Several results are known concerning the existence of multiple solutions for multipoint boundary value problems, and we refer the reader to the papers [13β16] and the references cited therein.

Here and in the sequel, will denote the Cartesian product of space for , that is, equipped with the norm where for .

We say that is a weak solution to (1.1) if and

for every .

A special case of our main result is the following theorem.

Theorem 1.1. *Let be two positive continuous functions such that the differential 1-form is integrable, and let be a primitive of such that . Fix , , and assume that
**
then there is such that for each , the problem
**
admits at least two positive classical solutions.*

The main aim of the present paper is to obtain further applications of [12, Theorem 2.6] (see Theorem 2.1 in the next section) to the system (1.1), and the obtained results are strictly comparable with those of [9β11], and here we wil give the exact collocation of the interval of positive parameters.

For other basic notations and definitions, we refer the reader to [17β26]. We note that some of the ideas used here were motivated by corresponding ones in [10].

#### 2. Main Results

Our main tool is a three critical points theorem obtained in [12] (see also [1, 2, 5, 27] for related results), which is a more precise version of Theorem 3.2 of [28], to transfer the existence of three solutions of the system (1.1) into the existence of critical points of the Euler functional. We recall it here in a convenient form (see [23]).

Theorem 2.1 (see [12, Theorem 2.6]). *Let be a reflexive real Banach space, be a coercive continuously GΓ’teaux differentiable and sequentially weakly lower semicontinuous functional whose GΓ’teaux derivative admits a continuous inverse on , be a continuously GΓ’teaux differentiable functional whose GΓ’teaux derivative is compact such that . Assume that there exist and , with such that**,
** for each , the functional is coercive.**
then, for each , the functional has at least three distinct critical points in .*

Put Since for , and the embedding is compact, one has . Moreover, from [10, ], one has

Put for . Let denotes the inverse of for . then, where . It is clear that is increasing on ,

Lemma 2.2 (see [10, Lemma 3.3]). *For fixed and , define by
**
then the equation
**has a unique solution .*

Direct computations show the following.

Lemma 2.3 (see [10, ]). *The function is a solution of the system (1.1) if and only if is a solution of the equation
**
for , where is the unique solution of (2.5).*

Lemma 2.4. *A weak solution to the systems (1.1) coincides with classical solution one. **Proof. *Suppose that is a weak solution to (1.1), so
for every . Note that, in one dimension, any weakly differentiable function is absolutely continuous, so that its classical derivative exists almost everywhere, and that the classical derivative coincides with the weak derivative. Now, using integration by part, from (2.7), we obtain
and so for ,
for almost every . Then, by Lemmas 2.2 and 2.3, we observe
for , where is the unique solution of (2.5). Hence, and for , namely is a classical solution to the system (1.1).

For all , we denote by the set Now, we formulate our main result as follows.

Theorem 2.5. *Assume that there exist constants for with and , a positive constant and a function such that *(A1) *,
*(A2)*where (see (2.11)),*(A3)* uniformly with respect to **Then, for each , the system (1.1) admits at least three distinct classical solutions in .**Proof. *In order to apply Theorem 2.1 to our problem, we introduce the functionals for each , as follows:
Since for , is compactly embedded in and it is well known that and are well defined and continuously differentiable functionals whose derivatives at the point are the functionals , , given by
for every , respectively, as well as is sequentially weakly upper semicontinuous. Furthermore, Lemma 2.6 of [11] gives that admits a continuous inverse on , and since is monotone, we obtain that is sequentially weakly lower semiacontinuous (see [29, Proposition 25.20]). Moreover, is a compact operator. From assumption (A1), we get . Since from (2.1) for each ,
for , we have
for each , and so using (2.15), we observe
and it follows that
Therefore, owing to assumption (A2), we have
Furthermore, from (A3), there exist two constants with
such that
Fix , Then
So, for any fixed , from (2.15) and (2.21), we have
and thus,
which means that the functional is coercive. So, all assumptions of Theorem 2.1 are satisfied. Hence, from Theorem 2.1 with , taking into account that the weak solutions of the system (1.1) are exactly the solutions of the equation and using Lemma 2.4, we have the conclusion.

Now we want to present a verifiable consequence of the main result where the test function is specified.

Put

Define where , then we have the following consequence of Theorem 2.5.

Corollary 2.6. *Assume that there exist constants for with and and two positive constants and with such that *(B1)* for each and ,*(B2)*ββ, where is given by (2.24) and (see (2.11));*(B3)*ββ uniformly with respect to .**then, for each the systems (1.1) admits at least three distinct classical solutions.*

*Proof. *Set such that for ,
and . It is easy to see that , and, in particular, one has
for , which, employing the condition , gives
Since for ,
the condition (B1) ensures that
Therefore, owing to assumption (B2), we have
where . Moreover, from assumption (B3) it follows that assumption (A3) is fulfilled. Hence, taking into account that
using Theorem 2.5, we have the desired conclusion.

Let us present an application of Corollary 2.6.

*Example 2.7. **Let * be the function defined as
for each . In fact, by choosing and , by a simple calculation, we obtain that and , and so with and , we observe that the assumptions (B1) and (B3) in Corollary 2.6 are satisfied. For (B2),
So, for every
Corollary 2.6 is applicable to the system
where .

Here is a remarkable consequence of Corollary 2.6.

Corollary 2.8. *Let be a function in such that . Assume that there exist constants for with and and two positive constants and with such that *(C1)* for each ,*(C2)*where is given by (2.24),*(C3)*,**Then, for each , the systems
**
for , admits at least three distinct classical solutions.*

*Proof. *Set for all and for . From the hypotheses, we see that all assumptions of Corollary 2.6 are satisfied. So, we have the conclusion by using Corollary 2.6.

*Example 2.9. *Let and , . Consider the system
Clearly, (H1) and (H2) hold. A simple calculation shows that and . So, by choosing and , we observe that the assumptions (C1) and (C3) in Corollary 2.8 hold. For (C3), since for every , we have
Note that . We see that for every
Corollary 2.8 is applicable to the system (2.38).

Finally, we prove the theorem in the introduction.

*Proof of Theorem 1.1. *Since and are positive, then is nonnegative in . Fix for some . Note that , and there is such that and
In fact, one has , where . Hence, there is such that
and .

from Corollary 2.8, with follows the conclusion.

#### Acknowledgment

The author would like to thank Professor Juan J. Nieto for valuable suggestions and reading this paper carefully.

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