# How to write letters in bold in the math mode?

In mathematics, a letter, say, g, can stand for a scalar, while a letter in bold, e.g., g stands for a vector.

Here is my question:

How can one turn the letter into bold in the math mode?

For example, how can I turn g here into bold?

$$-\nabla p+\mu\nabla^2u+g\delta(x-x_0)=0$$

• It is preferrable to use $ and $ as discussed here. Also see this for more on bold math symbols. – Peter Grill Jul 9 '11 at 2:31

Using the bm package. The \mathbf command can only be used for non-italic symbols, instead the amsmath package defines the \boldsymbol command that can be used with every literal symbol or math operator. The bm package redefines the \boldsymbol command providing the \bm command and is independent from amsmath. So you can use:

\documentclass{article}
\usepackage{amsmath}
\usepackage{bm}
\begin{document}
$\boldsymbol{g} \qquad \bm{g}$
\end{document}

• For non-italics, it is \mathrm{\mathbf{j}} – khaverim May 25 at 15:00

Use \mathbf{g} for bold in math mode.

• \mathbf doesn't work for everything – pratnala Feb 16 '16 at 4:01
• @pratnala That's true, but that also wasn't what the question was asking. See the accepted answer for a more general solution. – godbyk Feb 18 '16 at 18:31