Possible Duplicate:
Absolute Value Symbols
What is a correct way to write norm of a vector (or an operator)?
Is there a substantial difference between the following possibilities? Which of them do you recommend?
\newcommand{\norm}[1]{\lVert#1\rVert}
\newcommand{\norm}[1]{\|#1\|}
\newcommand{\norm}[1]{\left\|#1\right\|}
