English

Carl's inequality for quasi-Banach spaces

Functional Analysis 2016-05-24 v2

Abstract

We prove that for any two quasi-Banach spaces XX and YY and any α>0\alpha>0 there exists a constant γα>0\gamma_\alpha>0 such that sup1knkαek(T)γαsup1knkαck(T) \sup_{1\le k\le n}k^{\alpha}e_k(T)\le \gamma_\alpha \sup_{1\le k\le n} k^\alpha c_k(T) holds for all linear and bounded operators T:XYT:X\to Y. Here ek(T)e_k(T) is the kk-th entropy number of TT and ck(T)c_k(T) is the kk-th Gelfand number of TT. For Banach spaces XX and YY this inequality is widely used and well-known as Carl's inequality. For general quasi-Banach spaces it is a new result.

Keywords

Cite

@article{arxiv.1512.04421,
  title  = {Carl's inequality for quasi-Banach spaces},
  author = {Aicke Hinrichs and Anton Kolleck and Jan Vybiral},
  journal= {arXiv preprint arXiv:1512.04421},
  year   = {2016}
}

Comments

13 pages, minor changes suggested by referee, accepted for publication in Journal of Functional Analysis