Numerical index with respect to an operator
Tom 225 / 2014
Studia Mathematica 225 (2014), 165-171 MSC: Primary 47A12; Secondary 46E15, 46B20, 46B10. DOI: 10.4064/sm225-2-3
We introduce new concepts of numerical range and numerical radius of one operator with respect to another one, which generalize in a natural way the known concepts of numerical range and numerical radius. We study basic properties of these new concepts and present some examples.