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Themistocles M. Rassias

Publications and source records attributed to Themistocles M. Rassias.

5 recordsLinked to original sources
arXiv2020

Hyperstability of orthogonally 3-Lie homomorphism: an orthogonally fixed point approach

In this paper, by using the orthogonally fixed point method, we prove the Hyers-Ulam stability and the hyperstability of orthogonally 3-Lie homomorphisms for additive $ρ$-functional equation in 3-Lie algebras.\\ Indeed, we investigate the Hyers-Ulam stability and the hyperstability of the system of functional equations \begin{eqnarray*} \left\{ \begin{array}{ll} f(x+y)-f(x)-f(y)= ρ(2f(\frac{x+y}{2})+ f(x)+ f(y)),\\ f([[x,y],z])=[[f(x),f(y)],f(z)] \end{array} \right. \end{eqnarray*} in 3-Lie algebras (where $ρ$ is a fixed real number with $ρ\ne 1$).

math.FA↗
arXiv2019

An inequality related to Möbius transformations

The open unit ball $\mathbb{B} = \{\mathbf{v}\in\mathbb{R}^n\colon\|\mathbf{v}\|<1\}$ is endowed with Möbius addition $\oplus_M$ defined by $$\mathbf{u}\oplus_M\mathbf{v} = \dfrac{(1 + 2\langle\mathbf{u},\mathbf{v}\rangle + \|\mathbf{v}\|^2)\mathbf{u} + (1 - \|\mathbf{u}^2)\mathbf{v}}{1 + \langle\mathbf{u},\mathbf{v}\rangle + \|\mathbf{u}\|^2\|\mathbf{v}\|^2\|}$$ for all $\mathbf{u},\mathbf{v}\in \mathbf{B}$. In this article, we prove the inequality $$ \dfrac{\|\mathbf{u}\|-\|\mathbf{v}\|}{1+\|\mathbf{u}\|\|\mathbf{v}\|}\leq \|\mathbf{u}\oplus_M \mathbf{v}\| \leq \dfrac{\|\mathbf{u}\|+\|\mathbf{v}\|}{1-\|\mathbf{u}\|\|\mathbf{v}\|} $$ in $\mathbb{B}$. This leads to a new metric on $\mathbb{B}$ defined by $$d_T(\mathbf{u},\mathbf{v}) = \tan^{-1}{\|-\mathbf{u}\oplus_M\mathbf{v}\|},$$ which turns out to be an invariant of Möbius transformations on $\mathbb{R}^n$ carrying $\mathbb{B}$ onto itself. We also compute the isometry group of $(\mathbb{B}, d_T)$ and give a parametrization of the isometry group by vectors and rotations.

math.MG↗