Ho can I declare a math operator which will appear in bold font?

I tried the following, but it didn't work:


3 Answers 3


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


produces a medium weight ‘x’.

So you have to define


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:

  • That works, so you could define \DivB as a bold version of \Div for 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 H
    Sep 24, 2013 at 14:10

An alternative approach is to use \boldsymbol:

Sample output



\( \Div \)

\( \Divxk \)
  • The spacing is wrong; try $a\Divxk b$, where the operator nature is lost. It should be \mathop{\mathbf{Div}}_{X/k}.
    – egreg
    Sep 24, 2013 at 14:55
  • @egreg Of course! Thanks for pointing that out. Answer updated. Sep 24, 2013 at 15:04

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