Does infinite norm function use singular value ?

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

Answer 1

[Steven Lord]

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.

[Jeremy Brossard]

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,