Delimiters

Many mathematical formulas group their components with so-called delimiters. Think of regular arithmetic where 2*(5+6) is something different than (2*5)+6. But the uses go much further than that. For example, in computer science, you index the element of a list or array with [index].

The regular symbols, such as parentheses ( () ) and braces ( {} ) work. But they don’t scale with the equation. They just use their regular symbol, math mode or not. A fraction, for example, is much taller than the symbols surrounding it, which looks ugly and messy.

To solve this, LaTeX provides the \left and \right commands. These need to be used together—always—and both need a certain delimiter right after it.

Between them, you are allowed to use as many \middle commands with other delimiters as you like.

 1\begin{equation*}
 2    \left( \frac{2}{3} \right)
 3\end{equation*}
 4
 5\begin{equation*}
 6     \left| x+y \right|
 7\end{equation*}
 8
 9\begin{equation*}
10    \left\{ x \in \mathbb{R}^3 \middle| x \not= 2 \right\}
11\end{equation*}

Custom Sizes

If you’re not satisfied with LaTeXs default stretching of your delimiters to the correct length, use the special symbol-sizing commands:

Note that these should be used instead of the \left and \right commands. (They also work for most other symbols, which you’ll learn in a later chapter.)

1\begin{equation*}
2    %Yes, this looks awful, it's just for demonstrative purposes
3    \Bigg( \frac{2}{3} \big)
4\end{equation*}