For a square matrix x, what is the difference between norm(x,2) and norm(x,'fro')? My understanding is that they should be the same, but when I try the example below, they are different. What equation is used for both?

x = [1,2,3;4,5,6;7,8,9]
norm(x,2)
norm(x,'fro')

Answer 1

[the cyclist]

They are not equal. A quick web search suggests to me that:

norm(x,2) = sqrt(sum(x(:).*x(:)))

norm(x,'fro') = sqrt(max(eig(x'*x)))

If this is "mission-critical" for you, don't just take my word for it.