Electron. J. Linear Algebra 16, 347-365, electronic only (2007)
Summary
Summary: Characterizations are obtained for Schur (Hadamard) multiplicative maps on complex matrices preserving the spectral radius, numerical radius, or spectral norm. Similar results are obtained for maps under weaker assumptions. Furthermore, a characterization is given for maps f satisfying kA ffi $Bk = kf(A)$ ffi $f(B)$k for all matrices A and B.
