Taylor and Francis Ltd.;Abingdon: Taylor & Francis
摘要:
摘要： Let be an -by- partial isometry whose numerical range is a circular disc with centre and radius . In this paper, we are concerned with the possible values of and . We show that must be if is at most and conjecture that the same is true for the general . As for the radius, we show that if , then the set of all possible values of is . Indeed, it is shown more precisely that for , , the possible values of are those in the interval . In the proof process, we also characterize -by- partial isometries which are (unitarily) irreducible. The paper is concluded with a question on the rotational invariance of nilpotent partial isometries with circular numerical ranges centred at the origin. 出版者： Abingdon: Taylor & Francis 出版日期： 2016-01-02 出處： Linear & multilinear algebra, 2016-01, Vol.64 (1), p.14-35 版權： 2015 Taylor & Francis 2015 版權： 2015 Taylor & Francis 識別號： ISSN: 0308-1087 識別號： EISSN: 1563-5139 識別號： DOI: 10.1080/03081087.2014.1003530
