[Tex/LaTex] How to write letters in bold in the math mode

boldmath-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?

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

Best Answer

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}
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