## LaTeX: Adding Your Own Paired Delimiters

I’ve come to use LaTeX extensively for typesetting my Mathematics homework. It just makes things so beautiful. And like the XHTML/CSS split, it really does encourage strong separation of content from presentation. One of the things I first hated about it though, is that I grew quickly tired of using `\left` and `\right` with brackets, parentheses, or anything that needed to be automatically be sized to its content.

And, as any good engineering student might, I sought to encourage my own laziness by finding a clever shortcut. After a few minutes of searching Google, I came across the `DeclarePairedDelimiter` command in the `mathtools` package. Its usage is fairly self-explanatory, as I’ll let the following demonstrate.

First, you need to load the `mathtools` package in your document header:

\usepackage{mathtools} |

Then you can create your own paired delimiters with the `DeclarePairedDelimiter` command:

\DeclarePairedDelimiter{\abs}{\lvert}{\rvert} \DeclarePairedDelimiter{\norm}{\lVert}{\rVert} \DeclarePairedDelimiter{\innerproduct}{\langle}{\rangle} |

Finally, you can use these new commands in math mode to more easily group your expression. (Append an asterisk to make LaTeX automatically insert the necessary `\left` and `\right` commands when you need the delimiters to resize according to their content.)

If \(a \lt 0\) and \(b \gt 0\), then \(\abs{a} = -a\), and so \(\abs*{\frac{a}{b}} = -\frac{a}{b}\). |

The norm of a vector \(v\), denoted \(\norm{v}\), is defined by \(\norm{v} = \sqrt{\innerproduct{v,v}}\). |

As a nice bonus, it increases readability of the LaTeX source tremendously, since it gives those grouped expressions some semantic name rather than just being a bunch of formatting. For instance with the above delimiters, `\left\lvert \frac{a}{b} \right\rvert` is more to type, and a lot less obviously an absolute value, than the simpler `\abs*{\frac{a}{b}}`.

Happy hacking!