23

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?

AboAmmar
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yuxuan
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2 Answers2

19

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}

enter image description here

Ulrike Fischer
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    Thank you, it works. But do you know why the $\mathbf{\sigma}$ not work? Is it because I lack some fonts that supports the $\mathbf{\sigma}$ – yuxuan Sep 30 '15 at 19:36
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    @yuxuan: sigma is defined in a way that it "switch back" to the normal font. You should use \mathbf only for normal chars, not for symbols. – Ulrike Fischer Sep 30 '15 at 20:35
6

Uf, Ulrike Fisher is faster than me ... so I will escape the same prepared solution and add one other possibilities, for symbols instead of \mathbf{..} you can use \boldsymbol{...}:

\documentclass[paper=a4, fontsize=12pt]{article} % A4 paper and 11pt
    \usepackage{amsmath,amsfonts,amsthm} % Math packages

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

You will get almost the same result: enter image description here

Zarko
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    The documentation of amsbsy (that's automatically loaded by amsmath) says that using bm is better. – egreg Sep 30 '15 at 23:38