Parametrizations of Positive Matrices With Applications
  This paper reviews some characterizations of positive matrices and discusses which lead to useful parametrizations. It is argued that one of them, which we dub the Schur-Constantinescu parametrization is particularly useful. Two new applications of it are given. One shows all block-Toeplitz states are PPT. The other application is to relaxation rates. 
M. C. Tseng, Hong Zhou and V. Ramakrishna