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I know \mathcal{ABC...}, but can't bold these

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6 Answers 6

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34

You can define your own math alphabet that accesses the Computer Modern symbol font in its bold weight.

\documentclass{article}

\DeclareMathAlphabet\mathbfcal{OMS}{cmsy}{b}{n}

\begin{document}
$\mathcal{A}$ $\mathbfcal{A}$
\end{document}

Example

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    What does each of the arguments do? I get a bold font that is different from the mathcal in the particular article latex format, was wondering how to modify to make them consistent. I suspect that I should change cmsy by some other font.
    – Blade
    Jan 3, 2021 at 21:46
22

You're going to need a font that contains bold calligraphic fonts. One possibility for fonts without it is to use the bm package.

\bm{\mathcal{ABCDEFGHIJKLMNOPQRSTUVWXYZ}}
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    This also works for bolding greek letters in math mode, e.g. \bm{\alpha}
    – Martin Tapankov
    Sep 6, 2010 at 15:46
6

In mathematical environment you may use \boldsymbol

here is my suggestion:

\documentclass[...]{...}
\usepackage{amsbsy,amsmath}
\newcommand{\bs}[1]{\boldsymbol{#1}}
\newcommand{\HH}{\bs{\mathcal{H}}}
\newcommand{\DD}{\bs{\mathcal{D}}}
\newcommand{\pd}[2]{\frac{\partial{#1}}{\partial{#2}}}
\begin{document}
$\nabla\times\HH-\pd{\DD}{t}=\bs{j}$
\end{document}
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5

Another option is to bite the bullet and use LuaTeX with OpenType math fonts. In Context mkiv you can use

\setupbodyfont[xits]

\starttext
${\bf\cal abc}$
\stoptext

To get bold calligraphic fonts. As a bonus you get lowercase calligraphic as well. I am sure that unicode-math for lualatex has something similar.

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    Yep: \setmathfont{xits-math.otf}...$\mathbfcal{abc}$. Can be used in XeLaTeX or LuaLaTeX.
    – Will Robertson
    Sep 7, 2010 at 4:34
4

In unicode-math, \mathbfcal or \symbfcal.

In mathalpha, which is compatible with PDFLaTeX, \mathbcal. This gives you a nearly-comprehensive selection of all available 8-bit fonts, with a consistent interface, and scaling.

Update: Version 1.14 and higher of mathalpha changed the command to \mathbfcal. The old name is available as an alias if you give it the [oldbold] package option.

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I find that \boldsymbol works (for both mathcal and greek letters!).

But I stumbled upon this question when it stopped working for me. Turns out the culprit was the breqn package; I was able to get my \boldsymbol{\mathcal{F}} to show up as a calligraphy F after removing \usepackage{breqn}.

\documentclass{article}

\usepackage{amsbsy,amsmath}
% \usepackage{breqn}

\begin{document}

$\boldsymbol{\mathcal{F}}$

\end{document}
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