How to Write a Piecewise Function in LaTeX
To write a piecewise function in LaTeX, load \usepackage{amsmath} and use the cases environment inside math mode. Put the expression, then &, then the condition (usually with \text{...}), and end each line with \\. LaTeX draws the left brace automatically.
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Example
\usepackage{amsmath}
\[
f(x) =
\begin{cases}
x^2 & \text{if } x \ge 0 \\
-x & \text{if } x < 0
\end{cases}
\]Frequently asked questions
Why are my conditions in italics?
Text in math mode is italic and drops spaces. Wrap words in \text{...} (from amsmath) so a condition like "if x >= 0" reads correctly.
How do I number a piecewise function?
cases is unnumbered as a block. Put it inside an equation environment to number the whole thing once, or add \tag{...} for a custom label.
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