Talk:Linear entropy

In motivation section, need to say something along the lines of "The linear entropy best approximates the Von Neumann entropy when the series parameter ${\mbox{Tr}}(\rho -1)\,$ is small. This is the regime where $\rho \,$ is nearly the unit matrix, i.e. is very mixed." But I'm actually not sure how exactly to think about a matrix parameter in the series being small. I guess since it's positive definite, the sum of eigenvalues would be appropriate? Njerseyguy (talk) 18:13, 30 June 2009 (UTC)