Latex Undefined control sequence. ...\bm

遇到Undefined control sequence问题

原来是\bm{\theta}无法识别

解决方法:

To use \boldsymbol (in math mode, of course), you need to load the amsmath package.

Alternatively, load the bm ("bold math") package and write \bm{\beta} (again in math mode, of course).

e,g,

\documentclass{article}
\usepackage{amsmath} % for \boldsymbol macro
\usepackage{bm}      % for \bm macro
\begin{document}
$\boldsymbol{\beta} = (\beta_1,\beta_2,\dots,\beta_n)$

$\bm{\beta} = (\beta_1,\beta_2,\dots,\beta_n)$
\end{document}