# Variational Analysis, Optimization, and Fixed Point Theory

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Abstract and Applied AnalysisVolume 2013 2013, Article ID 823070, 2 pages

Editorial

Department of Mathematics, Aligarh Muslim University, Aligarh 202 002, India

Department of Mathematical Sciences, The University of Texas at El Paso, El Paso, TX 79968, USA

Department of Mathematics, King Abdulaziz University, Jeddah 21589, Saudi Arabia

Center of General Education, Kaohsiung Medical University, Kaohsiung 807, Taiwan

Received 5 September 2013; Accepted 5 September 2013

Copyright © 2013 Qamrul Hasan Ansari et al. 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.

In the last two decades, the theory of variational analysis including variational inequalities VI emerged as a rapidly growing area of research because of its applications in nonlinear analysis, optimization, economics, game theory, and so forth; see, for example, 1 and the references therein. In the recent past, many authors devoted their attention to study the VI defined on the set of fixed points of a mapping, called hierarchical variational inequalities. Very recently, several iterative methods have been investigated to solve VI, hierarchical variational inequalities, and triple hierarchical variational inequalities. Since the origin of the VI, it has been used as a tool to study optimization problems. Hierarchical variational inequalities are used to study the bilevel mathematical programming problems. A triple level mathematical programming problem can be studied by using triple hierarchical variational inequalities.

The Ekeland’s variational principle provides the existence of an approximate minimizer of a bounded below and lower semicontinuous function. It is one of the most important results from nonlinear analysis and it has applications in different areas of mathematics and mathematical sciences, namely, fixed point theory, optimization, optimal control theory, game theory, nonlinear equations, dynamical systems, and so forth, for example, 2–9 and the references therein. During the last decade, it has been used to study the existence of solutions of equilibrium problems in the setting of metric spaces, for example, 2, 3 and the references therein.

Banach’s contraction principle is remarkable in its simplicity, yet it is perhaps the most widely applied fixed point theory in all of analysis. This is because the contractive condition on the mapping is simple and easy to verify, and because it requires only completeness of the metric space. Although, the basic idea was known to others earlier, the principle first appeared in explicit form in Banach’s 1922 thesis where it was used to establish the existence of a solution to an integral equation.

Caristi’s fixed point theorem 10, 11 has found many applications in nonlinear analysis. It is shown, for example, that this theorem yields essentially all the known inwardness results of geometric fixed point theory in Banach spaces. Recall that inwardness conditions are the ones which assert that, in some sense, points from the domain are mapped toward the domain. This theorem is amazing equivalent to Ekeland’s variational principle.

Qamrul Hasan AnsariMohamed Amine KhamsiAbdul LatifJen-Chih Yao

References

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Author: **Qamrul Hasan Ansari, Mohamed Amine Khamsi, Abdul Latif, and Jen-Chih Yao**

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