The nonlinear alternative of the Leray Schauder type and the Banach contraction principle are used to investigate the existence of solutions for secondorder differential equations with integral boundary conditions. The compactness of solutions set is also investigated.
1. Introduction
This paper is concerned with the existence of solutions for the secondorder boundary value problem
where is a given function and is an integrable function.
Boundary value problems with integral boundary conditions constitute a very interesting and important class of problems. They include two, three, multipoint, and nonlocal boundary value problems as special cases. For boundary value problems with integral boundary conditions and comments on their importance, we refer the reader to the papers [1–9] and the references therein. Moreover, boundary value problems with integral boundary conditions have been studied by a number of authors, for example [10–14]. The goal of this paper is to give existence and uniqueness results for the problem (1.1). Our approach here is based on the Banach contraction principle and the LeraySchauder alternative [15].
2. Preliminaries
In this section, we introduce notations, definitions, and preliminary facts that will be used in the remainder of this paper. Let be the space of differentiable functions whose first derivative, , is absolutely continuous.
We take to be the Banach space of all continuous functions from into with the norm
and we let denote the Banach space of functions that are Lebesgue integrable with norm
Definition 2.1.
A map is said to be Carathéodory if
(i) is measurable for each
(ii) is continuous for almost each
(iii)for every there exists such that
3. Existence and Uniqueness Results
Definition 3.1.
A function is said to be a solution of (1.1) if satisfies (1.1).
In what follows one assumes that One needs the following auxiliary result.
Lemma 3.2.
. Let . Then the function defined by
is the unique solution of the boundary value problem
where
Proof.
Let be a solution of the problem (3.2). Then integratingly, we obtain
Hence
where
Now, multiply (3.6) by and integrate over , to get
Thus,
Substituting in (3.6) we have
Therefore
Set Note that
Our first result reads
Theorem 3.3.
Assume that is an Carathéodory function and the following hypothesis
(A1) There exists such that
holds. If
then the BVP (1.1) has a unique solution.
Proof.
Transform problem (1.1) into a fixedpoint problem. Consider the operator defined by
We will show that is a contraction. Indeed, consider Then we have for each
Therefore
showing that, is a contraction and hence it has a unique fixed point which is a solution to (1.1). The proof is completed.
We now present an existence result for problem (1.1).
Theorem 3.4.
Suppose that hypotheses
(H1) The function is an Carathéodory,
(H2) There exist functions and such that
are satisfied. Then the BVP (1.1) has at least one solution. Moreover the solution set
is compact.
Proof.
Transform the BVP (1.1) into a fixedpoint problem. Consider the operator as defined in Theorem 3.3. We will show that satisfies the assumptions of the nonlinear alternative of LeraySchauder type. The proof will be given in several steps.
Step 1 ( is continuous).
Let be a sequence such that in Then
Since is Carathéodory and then
Hence
Step 2 ( maps bounded sets into bounded sets in ).
Indeed, it is enough to show that there exists a positive constant such that for each one has .
Let . Then for each , we have
By (H2) we have for each
Then for each we have
Step 3 ( maps bounded set into equicontinuous sets of ).
Let , and be a bounded set of as in Step 2. Let and we have
As the righthand side of the above inequality tends to zero. Then is equicontinuous. As a consequence of Steps 1 to 3 together with the ArzelaAscoli theorem we can conclude that is completely continuous.
Step 4 (A priori bounds on solutions).
Let for some . This implies by that for each we have
Then
If we have
Thus
Hence
Set
and consider the operator From the choice of , there is no such that for some As a consequence of the nonlinear alternative of LeraySchauder type [15], we deduce that has a fixed point in which is a solution of the problem (1.1).
Now, prove that is compact. Let be a sequence in , then
As in Steps 3 and 4 we can easily prove that there exists such that
and the set is equicontinuous in hence by ArzelaAscoli theorem we can conclude that there exists a subsequence of converging to in Using that fast that is an Carathédory we can prove that
Thus is compact.
4. Examples
We present some examples to illustrate the applicability of our results.
Example 4.1.
Consider the following BVP
Set
We can easily show that conditions (A1), (3.14) are satisfied with
Hence, by Theorem 3.3, the BVP (4.1) has a unique solution on .
Example 4.2.
Consider the following BVP
Set
We can easily show that conditions (H1), (H2) are satisfied with
Hence, by Theorem 3.4, the BVP (4.4) has at least one solution on . Moreover, its solutions set is compact.
Acknowledgment
The authors are grateful to the referees for their remarks.
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