bm: Individual bold math symbols ¶Specifying \boldmath is the best method for typesetting a whole
math expression in bold, while to typeset individual symbols within an
expression in bold, the bm package provided by the LaTeX
Project team is better. Its usage is outside the scope of this
document (see its documentation at https://ctan.org/pkg/bm or in
your installation) but the spacing in the output of this small example
shows that it is an improvement over \boldmath within an
expression:
\usepackage{bm} % in preamble
...
we have $\bm{v} = 5\cdot\bm{u}$