# A System of Nonlinear Operator Equations for a Mixed Family of Fuzzy and Crisp Operators in Probabilistic Normed Spaces

- YeolJe Cho
^{1}, - Heng-you Lan
^{2}Email author and - Nan-jing Huang
^{3}

**2010**:152978

https://doi.org/10.1155/2010/152978

© Yeol Je Cho et al. 2010

**Received: **8 January 2010

**Accepted: **23 March 2010

**Published: **30 March 2010

## Abstract

By using a random version of the theory of contractor introduced by Altman, we introduce and study a system of nonlinear operator equations for a mixed family of fuzzy and crisp operators in probabilistic normed spaces. We construct some new iterative algorithms for solving this kind of nonlinear operator equations. We also prove some new existence theorems of solutions of a new system of nonlinear operator equations for a mixed family of fuzzy and crisp operators and some new convergence results of sequences generated by iterative algorithms under joint orbitally complete conditions.

## Keywords

## 1. Introduction

Altman [1, 2] introduced the theory of contractor and contractor direction, which has a very strong significant for the study of existence and uniqueness for solving nonlinear operator equations in Banach spaces. The theory of contractor offers a unified approach to a very large class of iterative methods including the most important ones. Chang [3] introduced the concept of probabilistic contractor and studied the existence and uniqueness of solution for nonlinear operator equations with probabilistic contractor in Menger PN-spaces. By using the theory of countable extension of -norms [4–6] and the results from [7, 8], many results for the more general classes of -norms have been proved (see [9] and the references therein).

On the other hand, since then, several kinds of variational inequalities, variational inclusions, complementarity problems, and nonlinear equations with fuzzy mappings were introduced and studied by many authors (see, e.g., [8–15]). Sharma et al. [15] considered two nonfuzzy mappings and a sequence of fuzzy mappings to define a hybrid -compatible condition. They also showed the existence of common fixed points under such condition, where the range of the one of the two nonfuzzy mappings is joint orbitally complete. Furthermore, Cho et al. [10] introduced the concept of probabilistic contractor couple in probabilistic normed spaces and discuss the solution for nonlinear equations of fuzzy mappings and the convergence of sequences generated by the algorithms in Menger probabilistic normed spaces. Very recently, Hadžić and Pap [16] introduced some new classes of probabilistic contractions in probabilistic metric spaces. They also obtained a new fixed point theorem for the -probabilistic contraction and gave some applications to random operators.

Motivated and inspired by the above works, in this paper, by using a random version of the theory of contractor introduced by Altman, we introduce and study a system of nonlinear operator equations for a mixed family of fuzzy and crisp operators in probabilistic normed spaces. We construct some new iterative algorithms for solving this kind of nonlinear operator equations. We also prove some new existence theorems of solution for the system of nonlinear operator equations for a mixed family of fuzzy and crisp operators and new convergence results of sequences generated by the iterative algorithms under joint orbitally complete condition. The results presented in this paper improve and generalize corresponding results of [9, 15–17].

## 2. Preliminaries

The ordered pair is said to be a probabilistic metric space if is a nonempty set and is written by for all satisfying the following conditions:

Recall that a mapping is a triangular norm (shortly, a -norm) if the following conditions are satisfied:

Example 2.1.

The following are the four basic examples.

If a -norm is such that then is a metrizable topological space under the -topology.

Let be a vector space over the real or complex number field , , and a -norm. The ordered triple is a Menger probabilistic normed space (briefly, a Menger PN-space) if and only if the following conditions are satisfied, where for all :

(i) for all and ( is a neutral element for in );

The following definition can be found in [7].

Definition 2.2 (see [7]).

Example 2.3 (see [9]).

It is easy to see that an ultra-metric space belongs to the class of N.A. Menger PN-spaces, where and satisfying the following conditions:

Let denote the collection of all fuzzy sets in such that is compact and convex for all and . For any , means for all .

Let be an arbitrary set and any linear metric space. A function is called fuzzy operator. Now, we define an orbit for mixed operators and a joint orbitally complete space as follows.

Definition 2.4 (see [15]).

then is called an orbit for the mixed operators .

Definition 2.5 (see [15]).

is called -joint orbitally complete if every Cauchy sequence of each orbit at is convergent in .

Remark 2.6 (see [15]).

Clearly, if is an any complete space and , then is -joint orbitally complete, while the converse is not necessarily true.

## 3. Some Countable -Norms

A -norm is of -type if the family is equicontinuous at (see [19]).

for any sequence in . Also, the sequence is nonincreasing and bounded from below and hence the limit exists.

The important classes of -norms are given in the following example.

Example 3.1 (see [16]).

The condition is fulfilled by the families , .

There exists a member of the family which is incomparable with and there exists a member of the family which is incomparable with .

In [4], the following results and proposition are obtained.

Proposition 3.2.

Let be a sequence of numbers from such that and a -norm of -type. Then

## 4. The Main Results

respectively.

Let be two fuzzy operators satisfying the following condition (I).

(I)There exist two mappings such that, for all , the set and .

In the sequel, for some , and are called the set-valued mappings induced by the fuzzy mappings and , respectively.

We need the following lemma and definitions.

Lemma 4.1 (see [7]).

Let be a Menger PN-space with a -norm satisfying and let . Then we have the following.

Definition 4.2.

Let and be two Menger PN-spaces. A set-valued mapping is said to be -closed if, for any and , whenever and , we have and .

Definition 4.3.

A function is said to satisfy the condition if it is nondecreasing and for all .

It is easy to prove that if satisfies the condition , then for all .

Definition 4.4 (see [7]).

Now, we introduce two algorithms for our main results as follows.

Algorithm 1.

Let be an N.A. Menger PN-space with a -norm and be a Menger PN-space with a -norm . Let , be two operators from into itself, a sequence of fuzzy operators from into satisfying the condition (I), and the -closed set-valued operators induced by the fuzzy operators for all . Let and satisfy the condition . Suppose that

(ii) for all and , for all and ;

(iii) is a probabilistic -contractor couple of and ;

Algorithm 2.

Let be a N.A. Menger PN-space with a -norm , a Menger PN-space with a -norm , and be two operators. Let a sequence of fuzzy operators from into satisfying the condition (I) and the set-valued operators induced by the fuzzy operators for all . Let and satisfy the condition . Suppose that the conditions (ii)–(iv) in Algorithm 1 are satisfied. If

where the sequence in is defined by (2.13).

Now, we state our main results by using the similar ideas as in [9].

Theorem 4.5.

Let be an N.A. Menger PN-space with a t-norm and be a Menger PN-space with a t-norm . Let , , , , , , and be the same as in Algorithm 1. Suppose that the conditions (i)–(iv) in Algorithm 1 hold and the following conditions are satisfied:

is -joint orbitally complete for some ;

where is a real nonnegative number.

has a solution such that . Further, -converges to a solution of (4.24) and -converges to , where in and in are two sequences generated by Algorithm 1.

Proof.

that is, is a solution of (4.24) and . This completes the proof.

From Theorem 4.5, we have the following.

Corollary 4.6.

Let be an N.A. Menger PN-space with a t-norm and a Menger PN-space with a -norm . Let , be two operators from into itself, a sequence of fuzzy operators from into satisfying the condition (I), and the -closed set-valued operators induced by the fuzzy operators for all . Let and satisfy the condition . Suppose that the conditions (i)-(iv) in Algorithm 1 and (v)-(vi) in Theorem 4.5 are satisfied. If -norm is of -type, then the conclusions of Theorem 4.5 still hold.

Proof.

By Proposition 3.2, we know that all the conditions of Theorem 4.5 are satisfied. Thus the conclusions of Theorem 4.5 still hold.

Corollary 4.7.

Let for some be a N.A. Menger PN-space and be a Menger PN-space. Let , be two operators from into itself, be a sequence of fuzzy operators from into satisfying the condition (I) and be the -closed set-valued operators induced by the fuzzy operators for all . Let and satisfy the condition . Suppose that the conditions (i)–(iv) in Algorithm 1 and (v)-(vi) of Theorem 4.5 are satisfied. If there exist and for some such that for all , where is a constant, then the conclusions of Theorem 4.5 still hold.

Proof.

Corollary 4.8.

Let for some be an N.A. Menger PN-space. Let , , , , , , , and be the same as in Theorem 4.5. Suppose that the conditions (i)–(iv) in Algorithm 1 and (v)-(vi) in Theorem 4.5 are satisfied. If there exist and for some such that for all , where is a constant, then the conclusions of Theorem 4.5 still hold.

Proof.

Remark 4.9.

it is easy to see that Corollary 4.8 is a generalization of the corresponding result in Fang [9].

Corollary 4.10.

Let for some be an N.A. Menger PN-space with a -norm . Let , , , , , , , and be the same as in Theorem 4.5. Suppose that the conditions (i)–(iv) in Algorithm 1 and (v)-(vi) of Theorem 4.5 are satisfied. If there exist and for some such that for all , where is a constant, then the conclusions of Theorem 4.5 still hold.

Proof.

Corollary 4.11.

Then there exists a point such that , that is, is a fixed point of .

Proof.

Putting for any fixed and , the mappings and satisfy all the hypotheses of Theorem 4.5. Therefore, there exists a point such that , which means that is a fixed point of . This completes the proof.

Theorem 4.12.

Let be an N.A. Menger PN-space with a -norm and be a Menger PN-space with a -norm . Let , , , , , , and be the same as in Algorithm 2. Suppose that the conditions (ii)–(iv) in Algorithm 1 and in Algorithm 2 are satisfied. If

is -joint orbitally complete for some ,

has a solution such that . Further, -converges to a solution of (4.40) and -converges to , where the sequences in and in are defined by Algorithm 2.

Proof.

Let and for all . It is obvious that all the conditions of Theorem 4.5 are satisfied. Therefore, the conclusion of Theorem 4.12 follows from Theorem 4.5 immediately.

Remark 4.13.

Similarly, we can obtain the conclusions of Theorem 4.12 if we replace the condition (iii) in Theorem 4.12 by the corresponding condition in Proposition 3.2 and the equivalences (3.10)–(3.12), respectively.

## Declarations

### Acknowledgments

This work was supported by the Korea Research Foundation Grant funded by the Korean Government (KRF-2008-313-C00050), the Sichuan Youth Science and Technology Foundation (08ZQ026-008), and the Open Foundation of Artificial Intelligence of Key Laboratory of Sichuan Province (2009RZ001).

## Authors’ Affiliations

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