If $A$ and $B$ are Hermitian matrices, then
$$r(A + B) \leq r(A) + r(B)$$
where $r$ denotes the spectral radius. Are there other standard conditions when this is true?
If $A$ and $B$ are Hermitian matrices, then
$$r(A + B) \leq r(A) + r(B)$$
where $r$ denotes the spectral radius. Are there other standard conditions when this is true?
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If $A,B$ are normal we have $r(A) = \lVert A \rVert$ and $r(B) = \lVert B \rVert$. Because in general we have $$ r(A+B) \leq \lVert A+B \rVert, $$ then $r(A+B) \leq r(A) + r(B)$ must hold.