41

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?

Hooked
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7 Answers7

38

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}"]
Community
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Andy Hayden
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  • This does not work: `ValueError: \boldsymbol{\phi} ^ Unknown symbol: \boldsymbol (at char 0), (line:1, col:1) ` perhaps it requires that we need `amsmath` loaded? Have you tested this on your machine? – Hooked Jan 14 '13 at 19:15
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    @Hooked I think including a preamble should work as described [here](http://www.inductiveload.com/posts/multi-line-latex-expressions-in-matplotlib/): `matplotlib.rc('text', usetex=True)`, `matplotlib.rcParams['text.latex.preamble']=[r"\usepackage{amsmath}"]`. Unfortunately I can't test yet, will update when I have. – Andy Hayden Jan 14 '13 at 19:52
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    On Matpotlib 3.3.3, with Python 3 7.13.0, adding those commands to rcParams leads to the following error, when trying to plot: `! LaTeX Error: File type1ec.sty not found.` – MRule Nov 23 '20 at 11:51
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    @MRule - See https://github.com/matplotlib/matplotlib/issues/16911 - On Debian and derivatives: `sudo apt install cm-super` - on macOS: `sudo tlmgr install cm-super` - on other systems: see packages listed at https://repology.org/projects/?search=cmsuper or https://repology.org/projects/?search=cm-super or https://repology.org/projects/?search=fontsrecommended – Samuel Lelièvre Dec 01 '21 at 12:52
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    `matplotlib.rcParams['text.latex.preamble']=[r"\usepackage{amsmath}"]` did not work for me (Python 3.9.9), but `matplotlib.rc('text.latex', preamble=r'\usepackage{amsmath}')` did! Thanks to [this post](https://stackoverflow.com/questions/41453109/how-to-write-your-own-latex-preamble-in-matplotlib#41453758) – Maze Dec 06 '21 at 04:03
  • In addition to `apt-get install cm-super`, I also had to `apt-get install dvipng`. With no additional changes, this provides the `\bf` symbol but not `\mathbf` or `\boldsymbol`. Adding then `rc('text', usetex=True); rc('text.latex',preamble=r"\usepackage{amsmath}")` makes both `\mathbf` and `\boldsymbol` available! It works! – MRule Jan 26 '22 at 13:46
18

If you intend to have consistently bolded fonts throughout the plot, the best way may be to enable latex and add \boldmath to your preamble:

# Optionally set font to Computer Modern to avoid common missing font errors
matplotlib.rc('font', family='serif', serif='cm10')

matplotlib.rc('text', usetex=True)
matplotlib.rcParams['text.latex.preamble'] = [r'\boldmath']

Then your axis or figure labels can have any mathematical latex expression and still be bold:

plt.xlabel(r'$\frac{\phi + x}{2}$')

However, for portions of labels that are not mathematical, you'll need to explicitly set them as bold:

plt.ylabel(r'\textbf{Counts of} $\lambda$'}
drs
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14

In case anyone stumbles across this from Google like I did, another way that doesn't require adjusting the rc preamble (and conflicting with non-latex text) is:

ax.set_ylabel(r"$\mathbf{\partial y / \partial x}$")
xiawi
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sodoesaburningbus
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1

When using LaTeX to typeset all text in a figure, you can make "normal" (non-equation) text bold by using \textbf:

ax.set_title(r"\textbf{some text}")
Blub Bla
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1

None of these solutions worked for me and I was astonished to find something so simple was so infuriating to achieve. In the end, this is what worked for my use case. I would advise adapting this for your own use:

plt.suptitle(r"$ARMA({0}, {1})$ Multi-Parameter, $\bf{{a}}$, Electrode Response".format(n_i, m), fontsize=16)

The {0} and {1} refer to positional arguments supplied to format method, meaning 0 refers to variable n_i and 1 refers to variable m.

Note: In my setup, for some reason, \textbf did not work. I have read somewhere that \bf is deprecated in LaTeX, but for me this is what worked.

Sameen
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0

As this answer Latex on python: \alpha and \beta don't work? points out. You may have a problem with \b so \boldsymbol may not work as anticipated. In that case you may use something like: '$ \\\boldsymbol{\\\beta} $' in your python code. Provided you use the preamble plt.rcParams['text.latex.preamble']=[r"\usepackage{amsmath}"]

Ahmad
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CJD
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  • Thank you for this input (on a 4 year old question!), but using `r` in front of a string should help escape the `\b`. The answer provided by @AndyHayden works fine and identifies the problem. – Hooked Jun 13 '17 at 21:40
0

I wanted to do something similar only then plot 'K' with subscript '1/2' as label and in bold. This worked without changing any of the rc parameters.

plt.figure()
plt.xlabel(r'$\bf{K_{1/2}}$')
JonnDough
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