Fixed point theorems for mixed monotone operators and applications to integral equations

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Abstract

The purpose of this paper is to present some coupled fixed point theorems for a mixed monotone operator in a complete metric space endowed with a partial order by using altering distance functions. We also present an application to integral equations.

Section snippets

Introduction and background

Mixed monotone operators were introduce by Guo and Lakshmikantham in [1]. Their study has not only important theoretical meaning but also wide applications in engineering, nuclear physics, biological chemistry technology, etc. (see [1], [2], [3], [4], [5], [6]).

The purpose of this paper is to present some coupled fixed point theorems for a mixed monotone operator in the context of ordered metric spaces involving altering distance functions. These theorems are generalizations of the results of

Coupled fixed point theorems

Let (X,) be a partially ordered set and d a metric on X such that (X,d) is a complete metric space. Further, we consider in the product space X×X the following partial order: if (x,y),(u,v)X×X,(x,y)(u,v)xu and yv. Now, we present the following theorem which is a version of Theorem 2.1 of [12] in the context of mappings with the mixed monotone property.

Theorem 2

Let (X,) be a partially ordered set and suppose that there exists a metric d in X such that (X,d) is a complete metric space. Let F:X×XX

Application to integral equations

In this section we study the existence and uniqueness of solutions of a nonlinear integral equation using the results proved in Section 2.

Consider the following integral equation: x(t)=01(k1(t,s)+k2(t,s))(f(s,x(s))+g(s,x(s)))ds+a(t),t[0,1]. We will analyze Eq. (28) under the following assumptions:

  • (i)

    ki:[0,1]×[0,1]R(i=1,2) are continuous and k1(t,s)0 and k2(t,s)0.

  • (ii)

    aC[0,1].

  • (iii)

    f,g:[0,1]×RR are continuous functions.

  • (iv)

    There exist constants λ,μ>0 such that for all x,yR and xy0f(t,x)f(t,y)λln[(yx)

Acknowledgement

This research was partially supported by “Ministerio de Educación y Ciencia”, Project MTM 2007/65706.

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