Does infinite norm function use singular value ?

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Jeremy Brossard
Jeremy Brossard 2020-6-5
编辑： darova 2020-6-13
Hello,
I would like to compute the infinite norm of the 2*2 following system : Q = [1/2+1j*sqrt(3)/2 -1 ; 1 2]
By hand I get :
In Matlab I write :
Q = [1/2+1j*sqrt(3)/2 -1 ; 1 2]
norm(Q,inf)
And I get a result of 3.
Why is the result different between Matlab and that one I calculated by hand?
I guess there is a question of rounding up with Matlab, if that is the case I did not find how to have more significant figures, how to do it?
Thanks,
Jeremy

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Steven Lord
Steven Lord 2020-6-5
As stated on the documentation page for the norm function and on Wikipedia, the infinity norm of a matrix is the maximum of its row sums. What you're computing is the 2-norm.
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Jeremy Brossard
Jeremy Brossard 2020-6-6
Ok it is a question of definition in that case because according to what I learnt max(svd(X)) is infinite norm and not 2-norm.
Thank you,

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