Bold font weight for LaTeX axes label in matplotlib

Question

In matplotlib you can make the text of an axis label bold by

plt.xlabel('foo',fontweight='bold') 

You can also use LaTeX with the right backend

plt.xlabel(r'$\phi$') 

When you combine them however, the math text is not bold anymore

plt.xlabel(r'$\phi$',fontweight='bold') 

Nor do the following LaTeX commands seem to have any effect

plt.xlabel(r'$\bf \phi$') plt.xlabel(r'$\mathbf{\phi}$') 

How can I make a bold $\phi$ in my axis label?

Answer 1

Unfortunately you can't bold symbols using the bold font, see this question on tex.stackexchange.

As the answer suggests, you could use \boldsymbol to bold phi:

r'$\boldsymbol{\phi}$' 

You'll need to load amsmath into the TeX preamble:

matplotlib.rc('text', usetex=True) matplotlib.rcParams['text.latex.preamble']=[r"\usepackage{amsmath}"]