FatalMath Mode
\boldsymbol Undefined (Missing bm or amsmath)
! LaTeX Error: \boldsymbol undefined.
What this error means
\boldsymbol is used to produce bold symbols in math mode, but it requires either the bm package (preferred) or amsmath. Without loading one of these, the command is undefined.
Common causes
- \boldsymbol used without \usepackage{bm} or \usepackage{amsmath}
- Using \mathbf{} as a substitute (which only works for Latin letters, not Greek)
How to fix it
Add \usepackage{bm} to your preamble. Use \bm{\symbol} instead of \boldsymbol{\symbol} — bm is the modern, recommended package. For simple Latin bold in math, \mathbf{x} works without any package.
Code examples
Causes the error
\documentclass{article}
% Missing \usepackage{bm}
\begin{document}
\[ \boldsymbol{\alpha} + \boldsymbol{x} = 0 \]
\end{document}Fixed
\documentclass{article}
\usepackage{bm}
\begin{document}
\[ \bm{\alpha} + \bm{x} = 0 \]
\end{document}Related errors
Test the fix live
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