Research Article | Open Access

Marian Matłoka, "A Note on -Convex Fuzzy Processes", *Advances in Fuzzy Systems*, vol. 2012, Article ID 290845, 4 pages, 2012. https://doi.org/10.1155/2012/290845

# A Note on -Convex Fuzzy Processes

**Academic Editor:**Salvatore Sessa

#### Abstract

We first define the concept of -convex fuzzy processes. Second, we present some basic properties of such processes.

#### 1. Introduction

In recent years, many generalizations of convexity have appeared in the literature aiming at applications to duality theory and optimality conditions. In 1997, Pini and Singh [1] introduced -convex functions and studied some of their properties. They showed that some of the well-known classes of generalized convex functions (e.g., B-vex functions [2], geodesic convex functions [3], and invex functions [4]) form subclasses of the class of -convex functions. In 1999, Youness [5] showed that many results for convex sets and convex functions actually hold for a wider class of sets and functions, called -convex sets and -convex functions.

Convex processes were studied first by Rockafellar [6] who was interested in extending properties of linear transformations to a large class of maps preserving convexity and which arise naturally in economic theory.

The extension of this notion to the fuzzy framework was done by Matłoka [7, 8] and was investigated by Syau et al. [9] and by Chalco-Cano et al. [10].

In this work, we extend the notion of -convex set, -convex fuzzy set, and -convex fuzzy process. First, we will present the preliminary definitions and next the main properties of -convex fuzzy process.

#### 2. Preliminaries

Let denote a subset of the -dimensional Euclidean space . Assume that is a map satisfying the following assumption:(i),(ii), , , .

For any subsets , of let us define

*Definition 1 (see [1]). *A set is -convex if for all , .

*Remark 2. *The intersection of -convex sets is still -convex.

*Remark 3. *Let be a convex subset of , and . Then a convex set is -convex.

*Remark 4. *If, is a preinvex set with respect to (see [11]), , then is a -convex set.

Assume that .

*Definition 5 (see [5]). *A set is said to be -convex if , for each and .

*Definition 6. *A set is said to be -convex if , for each and .

*Remark 7. *If and is the identity map then a convex set is -convex.

*Definition 8. *Let be a -convex set. A function is said to be -quasiconcave on if for any and
Let denote a fuzzy set in .

*Definition 9. *A fuzzy set is called -convex if and only if
for all .

*Definition 10. *An -cut of a fuzzy set is defined as follows:

Proposition 11. *If is -convex fuzzy set then is -convex (crisp) set.*

* Proof. *We have to prove that if then for any , . So, taking into account the above definitions, we observe that if then and and . So, . This means that .

#### 3. Main Results

In this section, we present the definition and some properties of the -convex fuzzy processes.

Let denote -convex set and the set of all non-void fuzzy sets in .

*Definition 12. *A mapping from to is called -convex fuzzy process if and only if for any and and

*Example 13. *Let , and let , , , and
Consider defined by
where , , and denotes the characteristics function of .

Then a mapping is -convex fuzzy process.

Now, let us consider defined by
for all and
for , where , .

The above mapping is -convex fuzzy mapping too.

Theorem 14. *If is a -convex fuzzy process from to and is an identity mapping then for any is a -convex fuzzy set in .*

* Proof. *We will prove that if , then for any
Let us note that for any .

So, using the definition of -convex fuzzy processes, we have

*Definition 15. *The graph of a -convex fuzzy process from to , denoted , is a fuzzy set in such that for any

In the analogous way as in the Definition 9, we can define the -convex fuzzy subset of , that is, for , , .

Theorem 16. *The graph of a -convex fuzzy process from to is a -convex fuzzy subset of .*

* Proof. *Taking into account the definitions of the graph and -convex fuzzy process, we observe that for any and

*Definition 17. *A composition of -convex fuzzy process from to and -convex fuzzy process from to is mapping from to such that
for any .

Theorem 18. *If is -convex fuzzy process from to and is -convex fuzzy process from to , then is a -convex fuzzy process from to .*

* Proof. *Let and . Then for any we have
So, is a -convex fuzzy process.

For any set , we put
for any .

Theorem 19. *If is -convex fuzzy process from to and is a -convex subset of and is an identity mapping then is -convex subset of .*

* Proof. *Let and . Then we have
So, is a -convex fuzzy subset of .

Theorem 20. *If is -convex fuzzy process from to then for any **
for any , .*

*Proof. *According to the definition of -cut, we have
Moreover,
This means that if then , that is,

Now, for any and any -quasiconcave function , let us define a function

Theorem 21. *If is a -convex fuzzy process from to , then the function is -quasiconcave.*

* Proof. *Let , . Then we have

#### References

- R. Pini and C. Singh, “$(\mathrm{\Phi}{E}_{1},\mathrm{\Phi}{E}_{2})$-convexity,”
*Optimization*, vol. 40, no. 2, pp. 103–120, 1997. View at: Google Scholar - C. R. Bector and C. Singh, “B-vex functions,”
*Journal of Optimization Theory and Applications*, vol. 71, no. 2, pp. 237–253, 1991. View at: Publisher Site | Google Scholar - T. Rapcsák, “Geodesic convexity in nonlinear optimization,”
*Journal of Optimization Theory and Applications*, vol. 69, no. 1, pp. 169–183, 1991. View at: Publisher Site | Google Scholar - M. A. Hanson, “On sufficiency of the Kuhn-Tucker conditions,”
*Journal of Mathematical Analysis and Applications*, vol. 80, no. 2, pp. 545–550, 1981. View at: Google Scholar - E. A. Youness, “E-convex sets, E-convex functions, and E-convex programming,”
*Journal of Optimization Theory and Applications*, vol. 102, no. 2, pp. 439–450, 1999. View at: Google Scholar - R. T. Rockafellar, “Monotone process of convex and concave type,”
*Amer. Math. Soc.*, no. 77, 1967. View at: Google Scholar - M. Matłoka, “Convex fuzzy processes,”
*Fuzzy Sets and Systems*, vol. 110, no. 1, pp. 104–114, 2000. View at: Google Scholar - M. Matłoka, “Some properties of Φ-convex fuzzy processes,”
*The Journal of Fuzzy Mathematics*, vol. 7, pp. 701–706, 1999. View at: Google Scholar - Y.-R. Syau, C. Y. Low, and T. H. Wu, “A note on convex fuzzy processes,”
*Applied Mathematics Letters*, vol. 15, no. 2, pp. 193–196, 2002. View at: Google Scholar - Y. Chalco-Cano, M. A. Rojas-Medar, and R. Osuna-Gómez, “s-convex fuzzy processes,”
*Computers and Mathematics with Applications*, vol. 47, no. 8-9, pp. 1411–1418, 2004. View at: Publisher Site | Google Scholar - T. Weir and B. Mond, “Pre-invex functions in multiple objective optimization,”
*Journal of Mathematical Analysis and Applications*, vol. 136, no. 1, pp. 29–38, 1988. View at: Google Scholar

#### Copyright

Copyright © 2012 Marian Matłoka. 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.