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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?

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3  
warning: if the default computer modern fonts are used, the weight of bold lowercase greek will not appear as bold as that of bold lowercase roman, and it isn't. default bold math (\mathbf} with computer modern fonts uses the font cmbx* which is an extended font. \boldsymbol or bm use the only cm font that is usually available in bold, cmmib10, which is not an extended font. thus the bold greek letters are indeed not as "bold" as the roman. –  barbara beeton Aug 26 '12 at 21:45

6 Answers 6

up vote 82 down vote accepted

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).

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I would vote for the bm package surely! –  tohecz Aug 26 '12 at 11:11

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

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2  
Why is \boldsymbol preferred over \boldmath? –  drs May 18 '13 at 1:18
2  
@drs \boldsymbol is included in the package amsmath, which is ubiquitous, while \boldmath is not. –  glarrain Jan 9 at 19:24

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

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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}

output

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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.

bold math overview

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ehm bm ehm. Can you underline "experience" with facts about problems of bm? –  tohecz Feb 21 '13 at 17:32
    
@tohecz No, unfortunately not. I don't have the particular example anymore. I just happened to stumble on this old question and I thought I'd add this list since I did encounter tricky cases where it was helpful to be able to try different approaches. bm should surely be the first package to try though. I will add examples where it doesn't work when it ever happens again. –  Christian Feb 21 '13 at 17:48

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}

gives

enter image description here

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Welcome to TeX.SX. –  Claudio Fiandrino Mar 27 '13 at 10:55
    
Welcome to TeX.sx! Rather than posting identical answers to different questions, you should post your answer at the most appropriate place (here: tex.stackexchange.com/a/104524/510) and (as soon as you have 50 rep) add comments with links at other places. –  lockstep Mar 27 '13 at 10:55

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