Operator version of the best approximation problem in Hilbert C*-modules

izvorni znanstveni rad

izvorni znanstveni rad

Operator version of the best approximation problem in Hilbert C*-modules

Vrsta prilog u časopisu
Tip izvorni znanstveni rad
Godina 2014
Časopis Journal of mathematical analysis and applications
Nadređena publikacija Journal of mathematical analysis and applications
Volumen 413
Svesčić 1
Stranice str. 311-320
DOI 10.1016/j.jmaa.2013.11.058
ISSN 0022-247X
EISSN 1096-0813
Status objavljeno

Sažetak

Let V⊆B(H, K) be a Hilbert C*-module over a C*- algebra A⊆B(H), and X, Y∈V. In this paper we study a problem of finding A∈B(H) such that |X+YB|- |X+YA| is a positive element in A for all B∈A. We show that such an operator exists if and only if the range of Y*X is contained in the range of Y*Y, and in this case it can be chosen to belong to A″. We also consider Hilbert C*-modules in which for every X and Y there is (a unique) A with the above property.

Ključne riječi

C*-algebra ; Hilbert C*-module ; Best approximation ; Closed range operator