Pretty good measurement (PGM)

For ensemble $\{p_j,{\rho }_j\}$ with average $\bar{\rho }={\sum }_j{p}_j{\rho }_j$, the pretty good measurement has $M_j={\bar{\rho }}^{-1/2}{p}_j{\rho }_j{\bar{\rho }}^{-1/2}$ on the support of $\bar{\rho }$.