http://upload.wikimedia.org/math/7/7...8706d780f6.png
What do the two lines on each side of the vectors mean?
http://upload.wikimedia.org/math/7/7...8706d780f6.png
What do the two lines on each side of the vectors mean?
those aren't absolute values, those are norms.
See
http://en.wikipedia.org/wiki/Norm_(mathematics)