This test probably has little meaning. (At least, Matlab is not smart enough to see that I take max of the same vector thousand times.) I guess, the difference is because the vector remains in a cache closer to the cpu. If speed is important, you might want to make a more realistic test.
N = 1000;
M = rand(1e5,N);
v = M(:,1);
tic
for jj = 1 : N
m = max(M(:,jj));
end
toc
tic
for jj = 1 : N
m = max(v);
end
toc
returns
Elapsed time is 0.465941 seconds.
Elapsed time is 0.036675 seconds.
.
One column only:
N = 1000;
M = rand(1e5,N);
v = M(:,1);
JJ = floor(N/2);
tic
for jj = 1 : N
m = max( M( :, JJ ) ); % <<<<<<<<<<<
end
toc
tic
for jj = 1 : N
m = max(v);
end
toc
returns
Elapsed time is 0.340061 seconds.
Elapsed time is 0.046989 seconds.
