WANAMBISI, MRWAFULAATHURW.
2010.
Invariance of numerical range under isometric transformation. African Journal Of Mathematics and Computer Science Research. : Academic Journals
AbstractIn this paper,we look at some properties of isometries and conditionsfor a quasi-affinity to be unitary.Among other results it is proved that if Ais a partial isometry such that if zero belongs to the numerical range of A or its positve integral powers then A is unitary