For a hermitian matrix R and a diagonal one Q, is there any relationship between eigenvalues/eigenvectors of R and QRQ? To be specific, assuming the eigenvalue decomposition of R is R=VDV*, then can the eigenvalues/eigenvectors of QRQ be represented by V, D & Q? Thanks a lot! *In fact I've ask [this question][1] on math.stackexchange already, and was advocated to ask here. I do hope to get a proof for it.* [1]: http://math.stackexchange.com/questions/682232/relationship-of-eigenvalue-eigenvector-of-hermitian-matrix-r-and-qrq-q-is-diago/682297?noredirect=1#comment1445742_682297