FatalCommands & Packages
Environment align Undefined (Missing amsmath)
! LaTeX Error: Environment align undefined.
What this error means
The align environment (and related environments like gather, multline, align*) are provided by the amsmath package. Without loading it, LaTeX has no definition for these environments.
FormaTeX smart compile
FormaTeX smart compile automatically detects align, gather, multline, and other AMS environments and injects \usepackage{amsmath} into the preamble before compiling.
Common causes
- \usepackage{amsmath} missing from the preamble
- Using align, gather, multline, alignat, flalign, or aligned without amsmath
- The preamble was accidentally edited and the amsmath line removed
How to fix it
Add \usepackage{amsmath} to your preamble. If you use any AMS math environments or commands (\text{}, \intertext{}, \tfrac{}, etc.), amsmath is required.
Code examples
Causes the error
\documentclass{article}
% Missing \usepackage{amsmath}
\begin{document}
\begin{align}
a &= b + c \\
d &= e - f
\end{align}
\end{document}Fixed
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
a &= b + c \\
d &= e - f
\end{align}
\end{document}Related errors
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