References
- [1] T. Aoki, On the stability of the linear transformation in Banach spaces, J. Math. Soc. Japan, 2 (1950), 64–66.
- [2] R. Badora, On some generalized invariant means and their application to the stability of the Hyers–Ulam type, Ann. Polon. Math., 58 (1993), 147–159.
- [3] S. Czerwik, K. Dlutek, Stability of the quadratic functional equation in Lipschitz spaces, J. Math. Anal. Appl., 293 (2004), 79–88.
- [4] H. Drygas, Quasi-inner products and their applications, in Advances in Multivariate Statistical Analysis, K. Gupta, Ed., Reidel (1987), 13–30.
- [5] B. R. Ebanks, P. I. Kannappan, P. K. Sahoo, A common generalization of functional equations characterizing normed and quasi-inner-product spaces, Can. Math. Bull., 35 (1992), 321–327.
- [6] Iz. EL-Fassi, Generalized hyperstability of a Drygas functional equation on a restricted domain using Brzdek’s fixed point theorem, J. Fixed Point Theory Appl., 19 (4) (2017), 2529–2540.
- [7] Iz. EL-Fassi, On approximation of approximately generalized quadratic functional equation via Lipschitz criteria, Quaest. Math., 42 (5) (2019), 651–663.
- [8] Iz. EL-Fassi, A. Chahbi, S. Kabbaj, Lipschitz stability of the k-quadratic functional equation, Quaest. Math., 40 (8) (2017), 991–1001.
- [9] G. L. Forti, Hyers–Ulam stability of functional equations in several variables, Aequationes Math., 50 (1995), 143–190.
- [10] G. L. Forti, J. Sikorska, Variations on the Drygas equation and its stability, Nonlinear Anal., 74 (2011), 343–350.
- [11] Z. Gajda, On stability of additive mappings, Int. J. Math. Math. Sci., 14 (1991), 431–434.
- [12] Z. Gajda, Invariant Means and Representations of Semi-groups in the Theory of Functional Equations, Prace Naukowe Uniwersytetu Ślaskiego, Katowice, 1992.
- [13] F. P. Greenleaf, Invariant Means on Topological Groups and Their Applications, in: Van Nostrand Mathematical Studies, vol.16, Van Nostrand, New York, 1969.
- [14] D. H. Hyers, On the stability of the linear functional equation, Proc. Nat. Acad. Sci. USA, 27 (1941), 222–224.
- [15] D. H. Hyers, G. Isac, Th. M. Rassias, Stability of Functional Equations in Several Variables, Birkhäuser, Boston, 1998.
- [16] S.-M. Jung, P. K. Sahoo, Stability of a functional equation of Drygas, Aequationes Math., 64 (2002), 263–273.
- [17] Th. M. Rassias, On the stability of the linear mapping in Banach spaces, Proc. Amer. Math. Soc., 72 (1978), 297–300.
- [18] P. K. Sahoo, P. Kannappan, Introduction to functional equations, CRC Press, Boca Raton, Fla, USA (2011).
- [19] J. Sikorska, On a direct method for proving the Hyers-Ulam stability of functional equations, J. Math. Anal. Appl., 372 (2010), 99–109.
- [20] J. Tabor, Lipschitz stability of the Cauchy and Jensen equations, Results Math., 32 (1997), 133–144.
- [21] S. M. Ulam, A Collection of Mathematical Problems, Interscience, New York, 1960.
- [22] D. Yang, Remarks on the stability of Drygas equation and the Pexider-quadratic equation, Aequat. Math., 68 (2004), 108–116.