### Setting bold Greek letters in LaTeX maths

The issue here is complicated by the fact that `\`

`mathbf`

(the
command for setting bold *text* in TeX maths) affects a select
few mathematical ‘symbols’ (the uppercase Greek letters).

In the default configuration, lower-case Greek letters behave
differently from upper-case Greek letters (the lower-case greek
letters are in the maths fonts, while the upper-case letters are in
the original (OT1-encoded) text fonts).

The Plain TeX solution *does* work, in a limited way; you set a
maths *style*, before you start an equation; thus

{\boldmath$\theta$}

does the job, but `\`

`boldmath`

may not be used in maths mode. As a
result, this solution requires that you embed single bold characters
in a text box:

$... \mbox{\boldmath$\theta$} ...$

which then causes problems in superscripts, etc. With
*amsmath* loaded,

$... \text{\boldmath$\theta$} ...$

does the trick (and is less bad in regard to superscripts, etc), but
is an unsatisfactory solution, too.

These problems may be addressed by using a bold mathematics package.

- The
*bm* package, which is part of the LaTeX tools
distribution, defines a command `\`

`bm`

which may be used anywhere
in maths mode.
- The
*amsbsy* package (which is part of AMSLaTeX)
defines a command `\`

`boldsymbol`

, which (though slightly less
comprehensive than `\`

`bm`

) covers almost all common cases.

All these solutions apply to all mathematical symbols, not merely
Greek letters.

*bm.sty*- Distributed as part of macros/latex/required/tools (or browse the directory); catalogue entry
*amsbsy.sty*- Distributed as part of AMSLaTeX macros/latex/required/amslatex (or browse the directory); catalogue entry
*amsmath.sty*- Distributed as part of AMSLaTeX
macros/latex/required/amslatex (or browse the directory); catalogue entry

*This answer last edited: 2013-06-12*

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