Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
5.3
2.2
Journals
Symmetry
Special Issues
Functional Equations and Inequalities: Topics and Applications
share announcement

Functional Equations and Inequalities: Topics and Applications

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Mathematics".

Deadline for manuscript submissions: closed (28 February 2026) | Viewed by 2819

Special Issue Editor

Dr. Włodzimierz Fechner

E-Mail Website
Guest Editor
Institute of Mathematics, Lodz University of Technology, al. Politechniki 8, 93-590 Łódź, Poland
Interests: functional equations; functional inequalities; fuzzy logic; Hyers-Ulam stability; classical analysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to invite you to contribute to this Special Issue on "Functional Equations and Inequalities: Topics and Applications". Functional equations and inequalities are pivotal in mathematics, providing essential tools for modelling and solving problems across a wide spectrum of scientific disciplines. Their study has led to significant theoretical breakthroughs and practical innovations, impacting fields from classical analysis and geometry to modern computer science and economics. Building on the continued interest and advancements in this area, this issue aims to capture the latest developments.

This Special Issue aims to present a collection of cutting-edge research that reflects the vibrancy and breadth of functional equations and inequalities. We seek to foster an exchange of ideas and showcase the power of these mathematical tools in addressing contemporary scientific challenges. The study of functional equations often involves inherent symmetries and structures, aligning well with the scope of many multidisciplinary and mathematical journals.

In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:

  • General solution methods for various types of functional equations and inequalities;
  • Stability of functional equations;
  • Functional equations on diverse algebraic and abstract structures (e.g., groups, Banach spaces, fuzzy settings);
  • Applications of functional equations and inequalities in mathematics, physics, economics, engineering, information theory, and other sciences;
  • Connections between functional equations and other mathematical disciplines such as operator theory, fixed point theory, and dynamical systems;
  • Iterative functional equations and functional differential/integral equations.

I look forward to receiving your contributions.

Dr. Włodzimierz Fechner
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • functional equations
  • functional inequalities
  • stability theory
  • Ulam stability
  • fixed point theory
  • difference equations
  • operator theory
  • applications of functional equations

Benefits of Publishing in a Special Issue

  • Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
  • Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
  • Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
  • External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
  • Reprint: MDPI Books provides the opportunity to republish successful Special Issues in book format, both online and in print.

Further information on MDPI's Special Issue policies can be found here.

Published Papers (4 papers)

Download All Papers
Order results
Result details
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:

Research

Jump to: Review

13 pages, 285 KB  
Article
On Solving Certain Functional Equations of Dynamic Programming in Relational-Metric Space Through a Non-Unique Fixed-Point Theorem
by Doaa Filali, Esmail Alshaban, Adel Alatawi, Bassam Z. Albalawi, Fahad M. Alamrani and Faizan Ahmad Khan
Symmetry 2026, 18(3), 486; https://doi.org/10.3390/sym18030486 - 12 Mar 2026
Viewed by 350
Abstract
This article aims to describe the solvability of certain functional equations related to dynamic programming by fixed-point theorems in relational-metric spaces. To achieve our goal, we exhibit a non-unique fixed-point finding for a map of the Ćirić type in a relational-metric space. In [...] Read more.
This article aims to describe the solvability of certain functional equations related to dynamic programming by fixed-point theorems in relational-metric spaces. To achieve our goal, we exhibit a non-unique fixed-point finding for a map of the Ćirić type in a relational-metric space. In this way, we consolidate and amend innumerable celebrated results in fixed-point theory. A couple of instances are supplied to emphasize the practical value of our findings. Full article
(This article belongs to the Special Issue Functional Equations and Inequalities: Topics and Applications)
15 pages, 275 KB  
Article
Hyers–Ulam–Rassias Stability of Reciprocal-Type Functional Equations: Comparative Study of Direct and Fixed Point Methods
by Heejeong Koh
Symmetry 2025, 17(10), 1626; https://doi.org/10.3390/sym17101626 - 1 Oct 2025
Cited by 2 | Viewed by 567
Abstract
In this paper, we investigate the Hyers–Ulam–Rassias stability of reciprocal functional equations in non-Archimedean fuzzy normed spaces by using both the direct method and the fixed point alternative. In addition, we study a modified reciprocal type functional equation within the same framework using [...] Read more.
In this paper, we investigate the Hyers–Ulam–Rassias stability of reciprocal functional equations in non-Archimedean fuzzy normed spaces by using both the direct method and the fixed point alternative. In addition, we study a modified reciprocal type functional equation within the same framework using Brzdȩk’s fixed point method. A brief remark is provided on the incidental role of symmetry in the structure of such functional equations. Finally, a comparative analysis highlights the distinctive features, strengths, and limitations of each approach. Full article
(This article belongs to the Special Issue Functional Equations and Inequalities: Topics and Applications)
14 pages, 330 KB  
Article
Sharp Bounds on Hankel Determinants for Starlike Functions Defined by Symmetry with Respect to Symmetric Domains
by Alina Alb Lupaş, Adel Salim Tayyah and Janusz Sokół
Symmetry 2025, 17(8), 1244; https://doi.org/10.3390/sym17081244 - 5 Aug 2025
Cited by 12 | Viewed by 971
Abstract
This work investigates the behavior of the coefficients of analytic functions within certain subclasses characterized by inherent symmetric structures. By leveraging deep connections with functions exhibiting positive real part properties, the approach introduces a modern analytical framework that links the studied coefficients to [...] Read more.
This work investigates the behavior of the coefficients of analytic functions within certain subclasses characterized by inherent symmetric structures. By leveraging deep connections with functions exhibiting positive real part properties, the approach introduces a modern analytical framework that links the studied coefficients to those of auxiliary functions with regulated behavior. This connection allows for the derivation of sharp estimates and facilitates computational treatment. The proposed method builds upon certain classical and modern coefficient inequalities. The study focuses on obtaining precise bounds for specific determinant expressions associated with initial, inverse, and inverse logarithmic coefficients, all within a subclass of starlike functions exhibiting internal symmetry aligned with a recently introduced canonical structure. This symmetric perspective reveals how geometric properties can lead to refined quantitative outcomes that enhance contemporary analytic theory. Full article
(This article belongs to the Special Issue Functional Equations and Inequalities: Topics and Applications)
►▼ Show Figures

Figure 1

Review

Jump to: Research

20 pages, 373 KB  
Review
Survey on Ulam Stability with Respect to n-Norms and (n, β)-Norms
by El-sayed El-hady, Anna Bahyrycz and Janusz Brzdęk
Symmetry 2026, 18(3), 411; https://doi.org/10.3390/sym18030411 - 26 Feb 2026
Cited by 1 | Viewed by 430
Abstract
This article is a survey of the results published so far on Ulam stability of functional equations in n-normed spaces and (n, β)-normed spaces. We present and examine them, highlighting some traps they contain and outlining potential straightforward generalizations. We [...] Read more.
This article is a survey of the results published so far on Ulam stability of functional equations in n-normed spaces and (n, β)-normed spaces. We present and examine them, highlighting some traps they contain and outlining potential straightforward generalizations. We also draw attention to certain symmetries present in the results discussed. In this way, we complement two earlier surveys on Ulam stability in two-normed spaces. Full article
(This article belongs to the Special Issue Functional Equations and Inequalities: Topics and Applications)
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-4
Back to TopTop