Package inputenc error unicode character u 2212

This blog post explains how plots from matplotlib can be exported to PGF files, which in turn can be imported into $LaTeX$ documents. All figures in this post are links that point to the source code used to generate them.

Motivation

Skip this part if you are already motivated, i.e. you know why you would want to export from matplotlib to LaTeX.

Suppose you have a Python script that produces a nice plot using matplotlib. You might save the plot with

plt.savefig('histogram.png', dpi=400)

and it will write a PNG file to the disk, which is ~141 KB in size (in the example).

However, importing this file as an image into a LaTeX document has some drawbacks. Most notably that

• the fonts of the document do not match the axes labels,
• the text is not searchable (“probability density” would not be found with ctrl+f),
• the image gets blurry when the reader zooms in, and
• it is comparably large in file size.

The solution to all four problems is exporting a PGF file from matplotlib, so LaTeX itself can take care of rendering the figure.

Exporting Matplotlib Plots

Adjust your matplotlib script by adding the following lines after import matplotlib:

matplotlib.use("pgf")
matplotlib.rcParams.update({
    "pgf.texsystem": "pdflatex",
    'font.family': 'serif',
    'text.usetex': True,
    'pgf.rcfonts': False,
})

Update the save command to write to .pgf

plt.savefig('histogram.pgf')

and make sure LaTeX is installed on the system. The command pdflatex is needed. On Mac brew cask install mactex does the job.

Running the script will output the histogram file in PGF format which can be imported with LaTeX.

Importing PGF with LaTeX

Place the PGF file in the LaTeX project folder and import it with the following code:

begin{figure}
    begin{center}
        input{histogram.pgf}
    end{center}
    caption{A PGF histogram from texttt{matplotlib}.}
end{figure}

The figure will appear in the document.

Adjusting the Plot Size

The PGF figure might be scaled undesirably, e.g. it can be too wide. In that case I found it helpful to determine the text width textwidth of the document with the command

usepackage{layouts}

[...]

printinunitsof{in}prntlen{textwidth}

and adjust the matplotlib figure based on that:

fig.set_size_inches(w=4.7747, h=3.5)

Scaling with matplotlib is better than scaling the entire PGF figure because the font sizes remain the same and match the text in the document.

References

• Blog post on the same topic by Sebastian Billaudelle
• TeX StackExchange Answer by blahdiblah: determining the text width in a document
• StackOverflow answer by Elenium: matplotlib rcParams configuration
• Matplotlib examples: histogram plot used in this post

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