Thanks a lot. Do you mean the two density operators are the same and connected through some transformations? Could you explain with a little more details?
I'm confused about the two density operators:
\rho=\sum_{i}\delta(r-r_{i}) and \rho=\sum_{i}|\psi_{i}>\rho_{ii}<\psi_{i}|
Is there anyone explaining this question to me? Thanks very much.