Defining a new function with argument and angular brackets

Question

I want to define a function in a LaTeX document. More precisely, I want to define a function, say \ang{x}, where x is any input, such that the output is \rangle x \langle. Is there a way to go about this using \newcommand, or any way at all, for that matter?

Answer 1

I normally use \DeclarePairedDelimiter from mathtools for something like this. The point is that with the starred version, the delimiters automatically scale.

You can use a lot of different brackets, and you can make the macro take multiple arguments.

\documentclass{article}
\usepackage{mathtools}
\DeclarePairedDelimiter\bra{\langle}{\rvert}
\DeclarePairedDelimiter\ket{\lvert}{\rangle}
\DeclarePairedDelimiterX\braket[2]{\langle}{\rangle}{#1,\delimsize\vert,\mathopen{}#2}
\DeclarePairedDelimiterX\inner[2]{\langle}{\rangle}{#1,#2}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}
\DeclarePairedDelimiter\norm{\lVert}{\rVert}
\DeclarePairedDelimiter\set{\lbrace}{\rbrace}
\begin{document}
\begin{align}
  \bra{a}       &= \bra{\frac{a}{1}}\
  \ket{a}       &= \ket{\frac{a}{1}}\
  \braket{a}{b} &= \braket{\frac{a}{1}}{\frac{b}{1}}\
  \inner{a}{b}  &= \inner{\frac{a}{1}}{\frac{b}{1}}\
  \abs{a}       &= \abs{\frac{a}{1}}\
  \norm{a}      &= \norm{\frac{a}{1}}\
  \set{a,b}     &= \set{\frac{a}{1},\frac{b}{1}}
\end{align*}
\end{document}

Answer 2

A straightforward way to define such a macro would be

\newcommand{\ang}[1]{\langle #1 \rangle}

If you need the sizes of the angle brackets to grow with the size of the argument, you might want to define \ang as

\newcommand{\ang}[1]{\mleft\langle #1 \mright\rangle}

where \mleft and \mright are macros provided by the mleftright package. Using \mleft and \mright instead of \left and \right has certain advantages, specifically in terms of the whitespace padding that would be inserted by TeX.

Either way, \ang takes one argument, which will be typeset surrounded by left-hand and right-hand angle brackets.

Answer 3

You might want to have a look at the bropd package.

It features the br{} command that is a little more advanced. I matches the size of the brackets and automatically uses round, square, or curly brackets.

\begin{equation}
    \frac{1}{2}\br{f\cdot\br{x \br{y+z} + \br{\frac{a}{b}+c} }+g}
\end{equation}