Ho can I declare a math operator which will appear in bold font?
I tried the following, but it didn't work:
\DeclareMathOperator{\Div}{Div}
\newcommand{\Divxk}{\mathbf{\Div}_{X/k}}
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3 Answers
The \mathbf around \Div does nothing, because \Div is translated internally to something like "choose the \mathrm font and typeset ‘Div’”. Math fonts don't inherit features from the context: \mathrm always corresponds to the upright text font in medium weight (or boldface) if \boldmath is in force.
You can check that
$\mathbf{\mathrm{x}}$
produces a medium weight ‘x’.
So you have to define
\DeclareMathOperator{\Div}{\mathbf{Div}}
\newcommand{\Divxk}{\Div_{X/k}}
The definition of \Div becomes “choose the \mathrm font and typeset ‘\mathbf{Div}’”, so, for the same reason as before, the boldface font will be chosen.
Try this:
\DeclareMathOperator{\Div}{\mathbf{Div}}
answered Sep 24, 2013 at 14:02
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That works, so you could define
\DivBas a bold version of\Divfor use as required, but that may not necessarily meet the OP's use case. The general question of why\mathbf{\SomeMathOperator}doesn't have the desired effect (and what to do about it) may be more interesting.– Chris HSep 24, 2013 at 14:10
An alternative approach is to use \boldsymbol:
\documentclass{article}
\usepackage{amsmath}
\DeclareMathOperator{\Div}{Div}
\newcommand{\Divxk}{\mathop{\boldsymbol{\Div}}_{X/k}}
\begin{document}
\( \Div \)
\( \Divxk \)
\end{document}
answered Sep 24, 2013 at 14:44
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The spacing is wrong; try
$a\Divxk b$, where the operator nature is lost. It should be\mathop{\mathbf{Div}}_{X/k}.– egregSep 24, 2013 at 14:55 -
@egreg Of course! Thanks for pointing that out. Answer updated. Sep 24, 2013 at 15:04