Undefined control sequence problem

It turns out that \bm{\theta} is not recognized

Solution:

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

Alternatively, load thebm(“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}