A+ CATEGORY SCIENTIFIC UNIT

Universal stability of Banach spaces for $\varepsilon $-isometries

Volume 221 / 2014

Lixin Cheng, Duanxu Dai, Yunbai Dong, Yu Zhou Studia Mathematica 221 (2014), 141-149 MSC: Primary 46B04, 46B20, 47A58; Secondary 26E25, 46A20, 46A24. DOI: 10.4064/sm221-2-3

Abstract

Let $X$, $Y$ be real Banach spaces and $\varepsilon >0$. A standard $\varepsilon $-isometry $f:X\rightarrow Y$ is said to be $(\alpha ,\gamma )$-stable (with respect to $T:L(f)\equiv \mathop {\overline {\rm span}}\nolimits f(X)\rightarrow X$ for some $\alpha , \gamma >0$) if $T$ is a linear operator with $\| T\| \leq \alpha $ such that $Tf-{\rm Id}$ is uniformly bounded by $\gamma \varepsilon $ on $X$. The pair $(X,Y)$ is said to be stable if every standard $\varepsilon $-isometry $f:X\rightarrow Y$ is $(\alpha ,\gamma )$-stable for some $\alpha ,\gamma >0$. The space $X$ $[Y]$ is said to be universally left [right]-stable if $(X,Y)$ is always stable for every $Y\ [X]$. In this paper, we show that universally right-stable spaces are just Hilbert spaces; every injective space is universally left-stable; a Banach space $X$ isomorphic to a subspace of $\ell _\infty $ is universally left-stable if and only if it is isomorphic to $\ell _\infty $; and a separable space $X$ has the property that $(X,Y)$ is left-stable for every separable $Y$ if and only if $X$ is isomorphic to $c_0$.

Authors

  • Lixin ChengSchool of Mathematical Sciences
    Xiamen University
    Xiamen 361005, China
    e-mail
  • Duanxu DaiSchool of Mathematical Sciences
    Xiamen University
    Xiamen 361005, China
    e-mail
  • Yunbai DongSchool of Mathematics and Computer
    Wuhan Textile University
    Wuhan 430073, China
    e-mail
  • Yu ZhouSchool of Fundamental Studies
    Shanghai University of Engineering Science
    Shanghai 201620, China
    e-mail

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