Dear Colleagues,

The aim of this Special Issue is to attract papers of leading researchers dealing with new trends in functional equations (FE). Potential topics include but are not limited to finding solutions of FE on restricted domains (cf., e.g., [3]), extending solutions from a restricted domain (cf., e.g., [4,5]), various types of stability including hyperstability, superstability, and quotient stability (see [2,7,9,10]) as well as related fixed point results (see [6]), means, separation, convexity, iteration theory (cf., e.g., [1,11,12]), connections to other areas of mathematics (e.g., functional analysis, approximation theory, differential and integral equations, nonlinear analysis), and real world applications (cf., e.g., [8]).

  We welcome high-quality manuscripts with new result as well as outstanding expository papers.

References

[1] J. Aczél, J. Dhombres, Functional Equations in Several Variables, Encyclopedia of Mathematics and its Applications v. 31, Cambridge University Press, 1989.

[2] R.P. Agarwal, J. Brzdęk, J. Chudziak, Stability problem for the composite type functional equations, Expositiones Math. 36 (2018), 178–196.

[3] A. Bahyrycz, J. Brzdęk, A note on d'Alembert's functional equation on a restricted domain, Aequationes Math. 88 (2014), 169–173.

[4] A. Bahyrycz, J. Brzdęk, E. Jabłońska, On extensions of the generalized cosine functions from some large sets, Publ. Math. Debrecen 89 (2016), 263–275.

[5] J. Brzdęk, E. Jabłońska, On extensions of the generalized Jensen functions on semigroups, Bull. Australian Math. Soc. 96 (2017), 110–116.

[6] J. Brzdęk, L. Cădariu, K. Ciepliński, Fixed point theory and the Ulam stability, J. Function Spaces 2014 (2014), Article ID 829419, 16 pp.

[7] J. Brzdęk, D. Popa, I. Rasa, B. Xu, Ulam Stability of Operators, Mathematical Analysis and its Applications v. 1, Academic Press, Elsevier, Oxford, 2018.

[8] E. El-hady, J. Brzdęk, H. Nassar, On the structure and solutions of functional equations arising from queueing models, Aequationes Math. 91 (2017), 445–477.

[9] D.H. Hyers, G. Isac, Th.M. Rassias, Stability of Functional Equations in Several Variables, Birkhäuser Boston, Boston, Mass, USA, 1998.

[10] S.-M. Jung, Hyers-Ulam-Rassias Stability of Functional Equations in Nonlinear Analysis, Springer, New York, NY, USA, 2011.

[11] M. Kuczma, An Introduction to the Theory of Functional Equations and Inequalities, 2^nd edition (A. Gilányi, ed.), Birkhäuser, Basel, 2009.

[12] M. Kuczma, B. Choczewski, R. Ger, Iterative Functional Equations, Cambridge University Press, Cambridge, UK, 1990.

Prof. Janusz Brzdęk
Prof. Liviu Cădariu
Dr. Eliza Jabłonska
Guest Editors

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• functional equation
• restricted domain
• extension of solution
• Ulam stability
• hyperstability
• superstability
• quotient stability
• fixed point
• mean
• separation
• convexity
• iteration theory