Components of Vectors

How do I represent the ordered pair representing a vector, without the usual open/close parentheses? My calculus textbook uses these:

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\langle a_1,a_2\rangle – David Carlisle Apr 27 '14 at 1:51
Welcome to TeX.SX! – Heiko Oberdiek Apr 27 '14 at 2:11
Thank you very much! – user50608 Apr 27 '14 at 2:17

\documentclass{article}
\usepackage{physics}
\usepackage{mathtools}
\DeclarePairedDelimiter{\opair}{\langle}{\rangle}
\begin{document}
Using \verb|mathtools| and its \verb|DeclarePairedDelimiter| macro

$\vb{a}=\opair{a,b}$

Using \verb|physics| and its \verb|expval| macro

$\vb{a}=\expval{a,b}$  or $\vb{a}=\ev{a,b}$
\end{document}


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?? Why not just use \documentclass{article}\begin{document}$\langle a,b\rangle$\end{document}? – msh210 Apr 27 '14 at 6:03
@msh210 Well, in first place, I think it's easier to write something like \ev{a,b} than \langle a,b \rangle. In second place you can teach the command (whichever you use) to enlarge the delimiters \ev{a,\frac{b}{g}} instead of \biggl\langle a,\frac{b}{g} \biggr\rangle. And last, and most important in my opinion, if you choose a good (semantic) name, you will read your code much more easily and, moreover, if you decide to change the appearance of whatever construction you are using, you only have to redefine the macro. – Manuel Apr 27 '14 at 9:09
@msh210 Well Manuel has already given the reason and I meant the same. – Harish Kumar Apr 27 '14 at 12:51

It looks like you're asking about form, not how to get the angle brackets, is that right?

I really don't like those angle brackets, because they tend to get used to mean other things (typically, the inner product).

Really, in my opinion, the best way to treat vectors is just like matrices (column or row vectors).

\mathbf{a} = \begin{bmatrix}a_x & a_y\end{bmatrix}'$ or \mathbf{a} = \begin{bmatrix}a_x\\a_y\end{bmatrix}  Alternatively, you can use element (unit) vectors \mathbf{a} = a_x \hat{x} + a_y \hat{y}.  There are many ways of writing the unit elements. The strictly mathy way is to use $\mathbf{\mathup{e}}_x$, or $\hat\i$. I prefer the column vectors. That way, dot products work out nicely as $\mathbf{a}'\mathbf{b}\$. For example, (noting that the prime indicates transposition)

Also, strictly speaking, the vectors should not be upright. They should be in bold italics. Upright symbols are reserved for mathematically defined quantities, such as pi, or e.

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