Canadian Mathematical Bulletin-Bulletin Canadien De Mathematiques
Let T be a quadratic operator on a complex Hilbert space H. We show that T can be written as a product of two positive contractions if and only if T is of the form aI circle plus bI circle plus [ GRAPHICS ] on H-1 circle plus H-2 circle plus (H-3 circle plus H-3) for some a, b is an element of [ 0, 1 ] and strictly positive operator P with parallel to P parallel to < = vertical bar root a - root b vertical bar root (1 - a) (1 - b). Also, we give a necessary condition for a bounded linear operator T with operator matrix [GRAPHICS] on H circle plus K that can be written as a product of two positive contractions.
Li, C. K., & Tsai, M. C. (2016). Factoring a quadratic operator as a product of two positive contractions. Canadian Mathematical Bulletin, 59(2), 354-362.