u={1,2,3} ; Sum[u]
This isn't giving 6: http://www.wolframalpha.com/input/?i=u%3D%7B1,2,3%7D+;+Sum%5Bu%5D
I think I'm doing it right: Sum
What gives?
Try this
u={1,2,3} sum components of u
http://www.wolframalpha.com/input/?i=u%3D%7B1,2,3%7D+sum+components+of+u