On the stability of mixed trigonometric functional equations.
On the Stability of Orthogonal Additivity
We deal with the stability of the orthogonal additivity equation, presenting a new approach to the proof of a 1995 result of R, Ger and the second author. We sharpen the estimate obtained there. Moreover, we work in more general settings, providing an axiomatic framework which covers much more cases than considered before by other authors.
On the stability of quadratic functional equations.
On the stability of solutions of certain systems of differential equations with piecewise constant argument
We obtain some sufficient conditions for the existence of the solutions and the asymptotic behavior of both linear and nonlinear system of differential equations with continuous coefficients and piecewise constant argument.
On the stability of some quadratic functional equation.
On the stability of the functional equation for polynomials.
On the stability of the quadratic functional equation in topological spaces.
On the stability of the quadratic mapping in normed spaces.
On the stability of the squares of some functional equations
We consider the stability, the superstability and the inverse stability of the functional equations with squares of Cauchy’s, of Jensen’s and of isometry equations and the stability in Ulam-Hyers sense of the alternation of functional equations and of the equation of isometry.
On the stability of trigonometric functional equations.
On the stabiltiy of a system of functional equations characterizing generalize hyperbolic and trigonometric functions.
On the structure of homoethic functions. (Summary).
On the structure of homothetic functions.
On the superstability of generalized d’Alembert harmonic functions
The aim of this paper is to study the superstability problem of the d’Alembert type functional equation f(x+y+z)+f(x+y+σ(z))+f(x+σ(y)+z)+f(σ(x)+y+z)=4f(x)f(y)f(z) for all x, y, z ∈ G, where G is an abelian group and σ : G → G is an endomorphism such that σ(σ(x)) = x for an unknown function f from G into ℂ or into a commutative semisimple Banach algebra.
On the superstability of the cosine and sine type functional equations
In this paper, we study the superstablity problem of the cosine and sine type functional equations: f(xσ(y)a)+f(xya)=2f(x)f(y) and f(xσ(y)a)−f(xya)=2f(x)f(y), where f : S → ℂ is a complex valued function; S is a semigroup; σ is an involution of S and a is a fixed element in the center of S.
On the superstability of the Pexider type trigonometric functional equation.
On the support of midconvex operators.
On the support of midconvex operators. (Summary).
On the System of Functional Equations f(x +y) = f(x) + f (y) and f(xy)=p(x)f(y)
On the System of Functional Equations. (Short Communication).