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Added a true bound for all matrices.
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Oscar Lanzi
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It certainly holds for all matrices where $|a_{ij}|=|a_{ji}|$ (meaning both symmetric and skew-symmetric matruces, among otbers). It is reported here that

$||A||_2^2\le||A||_1||A||_\infty,$

and where the condition above is satisfied $||A||_1=||A||_\infty$.


For all $n×n$ matrices we always have

$||A||_1\le n||A||_\infty$

$||A||_\infty\le n||A||_1$

and so the bound given above implies

$||A||_2\le\sqrt{n}||A||_1$

$||A||_2\le\sqrt{n}||A||_\infty.$

It certainly holds for all matrices where $|a_{ij}|=|a_{ji}|$ (meaning both symmetric and skew-symmetric matruces, among otbers). It is reported here that

$||A||_2^2\le||A||_1||A||_\infty,$

and where the condition above is satisfied $||A||_1=||A||_\infty$.

It certainly holds for all matrices where $|a_{ij}|=|a_{ji}|$ (meaning both symmetric and skew-symmetric matruces, among otbers). It is reported here that

$||A||_2^2\le||A||_1||A||_\infty,$

and where the condition above is satisfied $||A||_1=||A||_\infty$.


For all $n×n$ matrices we always have

$||A||_1\le n||A||_\infty$

$||A||_\infty\le n||A||_1$

and so the bound given above implies

$||A||_2\le\sqrt{n}||A||_1$

$||A||_2\le\sqrt{n}||A||_\infty.$

Source Link
Oscar Lanzi
  • 2.4k
  • 21
  • 20

It certainly holds for all matrices where $|a_{ij}|=|a_{ji}|$ (meaning both symmetric and skew-symmetric matruces, among otbers). It is reported here that

$||A||_2^2\le||A||_1||A||_\infty,$

and where the condition above is satisfied $||A||_1=||A||_\infty$.