clear
format compact

%%
A = [ 2  0; 1  -1 ]

%%
% The default norm returned by the |norm| command is the 2-norm.
twonorm = norm(A)

%%
% You can get the 1-norm as well.
onenorm = norm(A, 1)

%%
% The 1-norm is equivalent to 
max( sum(abs(A), 1) )   % sum along rows (1st matrix dimension)

%%
% Similarly, we can get the infinity-norm and check our formula for it.
infnorm = norm(A, inf)
max( sum(abs(A), 2) )   % sum along columns (2nd matrix dimension)