[Tex/LaTex] Why can’t I get a bold Greek letter?

Question

This question already has answers here:

How can I get bold math symbols?

(14 answers)

Closed 5 years ago.

My MWE is as follows:

\documentclass[paper=a4, fontsize=12pt]{article} % A4 paper and 11pt
 % font size
\usepackage[english]{babel} % English language/hyphenation
\usepackage{amsmath,amsfonts,amsthm} % Math packages

\begin{document}
    \begin{align*}
(\mathbf{n}\cdot \mathbf{\sigma}) \sigma&=\mathbf{0}
    \end{align*}
\end{document}

But the results show \mathbf{\sigma} and \sigma the same. Why?

Answer 1

You can use the bm-package

\documentclass[paper=a4, fontsize=12pt]{article} % A4 paper and 11pt
 % font size
\usepackage[english]{babel} % English language/hyphenation
\usepackage{amsmath,amsfonts,amsthm,bm} % Math packages

\begin{document}
    \begin{align*}
(\mathbf{n}\cdot \bm{\sigma}) \sigma&=\mathbf{0}
    \end{align*}
\end{document}