How can I get bold math symbols?

Question

To make Latin-letter variables bold I can use e.g. \mathbf{a}, but while putting Greek letters or symbols such as \nabla inside \mathbf doesn't cause any errors or warnings, it also doesn't do anything else.

What is the best way to make bold math symbols, in particular Greek letters and \nabla?

Answer 1

The AMS Short Math Guide recommends the \boldsymbol and \pmb commands (and suggests that you use the bm package for the former to get a more powerful version than provided by amsmath).

Answer 2

Another possibility is \boldmath, though I would prefer \boldsymbol of amsmath as well. \unboldmath switches back to the normal math font.

Answer 3

If you use the package bm you can do $\bm{a}=\bm{\alpha}$ etc.

Answer 4

For the sake of completeness, when using unicode-math, \mathbf works for both Greek and Latin letters. Compile with xelatex or lualatex.

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{xits-math.otf}
\begin{document}
\( AaBb∇αβγ \) \par
\( \mathbf{AaBb∇αβγ} \)
\end{document}

Answer 5

In my experience, there is no single best way. Therefore Table 327 on page 113 of the Comprehensive LaTeX Symbol List comes in really handy.

Answer 6

While \bm and \boldmath are some good options in LaTeX, modern packages for XeLaTex can give a lot more control over the fonts from the very beginning, without the need to use commands different from the standard \mathbf that every one expects naively to work the first time one tries to write bold italic characters.

In XeLaTeX (part of TeXLive), the package fontspec gives a lot of freedom when dealing with fonts. If you want even more flexibility for mathematical input, you can try using the package unicode-math (that is built on fontspec). Nevertheless you will find the \bm and \boldsymbol traditional commands don't work. You can nonetheless specify how you want it to deal with your bold math symbols using an option while loading the unicode-math package. \usepackage[bold-style=ISO]{unicode-math} will give the recommended italic bold math symbols for both greek and latin characters, while \usepackage[bold-style=TEX]{unicode-math} will give upright latin characters. This is explained in the unicode-math documentation .

This minimal working example:

%run this with XeLaTeX!!
\documentclass{article}
\usepackage[bold-style=ISO]{unicode-math}
%\usepackage[bold-style=TEX]{unicode-math}
\setmainfont{XITS}
\setmathfont{XITS Math}


\begin{document}

This is common math $O(\log n)+O(\lambda,\,\epsilon)$

This is bold and italic $\mathbf{O(\log n)}+\mathbf{O(\lambda,\,\epsilon)}$ where it must :)
\end{document}

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