A treatment of the Cauchy-Schwarz inequality in C*-modules

izvorni znanstveni rad

izvorni znanstveni rad

A treatment of the Cauchy-Schwarz inequality in C*-modules

Vrsta prilog u časopisu
Tip izvorni znanstveni rad
Godina 2011
Časopis Journal of mathematical analysis and applications
Volumen 381
Svesčić 2
Stranice str. 546-556
DOI 10.1016/j.jmaa.2011.02.062
ISSN 0022-247X
EISSN 1096-0813
Status objavljeno

Sažetak

We study the Cauchy-Schwarz and some related inequalities in a semi-inner product module over a C*-algebra A. The key idea is to consider a semi-inner product A-module as a semi-inner product A-module with respect to another semi-inner product. In this way, we improve some inequalities such as the Ostrowski inequality and an inequality related to the Gram matrix. The induced semi-inner products are also related to the the notion of covariance and variance. Furthermore, we obtain a sequence of nested inequalities that emerges from the Cauchy-Schwarz inequality. As a consequence, we derive some interesting operator-theoretical corollaries. In particular, we show that the sequence arising from our construction, when applied to a positive invertible element of a C*-algebra, converges to its inverse.

Ključne riječi

C*-algebra ; semi-inner product C*-module ; Cauchy-Schwarz inequality ; Gram matrix