Spectral norm is smaller than trace

679 Views Asked by At

How can I prove this inequality?

For any even number $k$ and symmetric matrix $A$,

$||A||^{k}\leq Tr(A^{k})$

where ||.|| stands form the spectral norm and $Tr$ for the trace of the matrix.

1

There are 1 best solutions below

3
On BEST ANSWER

This is true because for every real symmetric $A$, we have $\|A\|^{2k}\le\operatorname{tr}(A^{2k})$, or equivalently, $\left(|\lambda|_\max(A)\right)^{2k}\le\sum_i\lambda_i(A)^{2k}$.