Use of Hyphen or Minus Sign in Matplotlib versus Compatibility with Latex

Question

I am having the problem where a pgf created using matplotlib.pyplot outputs hyphens instead of minus signs, which Latex cannot interpret.

I attempted to use the solution found here, but it changes numbers from integers to floats (i.e. 2000 becomes 2000.0) in the tick labels. I am looking for a solution that fixes the signs but keeps the default formatting in pyplot otherwise.

Any ideas? Example below.

myplot.py

import matplotlib.pyplot as plt
from matplotlib.ticker import FuncFormatter

def math_formatter(x, pos):
    return "$%s$" % x 

plt.figure()
plt.plot([1,2,3,4,5,6,7],[-1,-2,3,4,5,6,7])

axis = plt.gca()
axis.xaxis.set_major_formatter(FuncFormatter(math_formatter))
axis.yaxis.set_major_formatter(FuncFormatter(math_formatter)) 

plt.show()

mylatex.tex

\documentclass{article}

\usepackage{pgf}

\begin{document}
    \begin{figure}[H]
        \centering
        \input{myplot.pgf}
     \end{figure}
\end{document}

If you plot without the formatter argument, you get the standard formatting as int, but latex will not recognize the hyphens as minus signs. If you use the formatter argument, all int will become floats.

I am looking for a solution where the hyphens are changed to minus signs but no matter the argument (int or float or otherwise) the ticks will behave like the default behavior of pyplot (except the hyphens are minus signs).

Answer 1

Recent versions of Matplotlib use, by default, the typographically "correct" (this is debatable) unicode minus signs (U+2212) to express negative numbers, and not the ASCII hyphens. On my system, the ASCII hyphen is interpreted without any problem in Latex, but the unicode minus sign is not by default.

Using a FuncFormatter with the expression return '%i' % x as you proposed here converts the minus sign to a hyphen and is a valid solution for Latex compatibility. In addition to this solution, below are two additional alternative solutions that could be used to solve this problem with a more "system-wide" approach.

matplotlib : use hyphen instead of minus sign

The ASCII hyphen (which is interpreted correctly by Latex by default) can be used instead of the unicode minus sign to express negative numbers in matplotlib. As per the documentation (http://matplotlib.org/1.3.0/examples/api/unicode_minus.html), it is possible to do this by doing:

matplotlib.rcParams['axes.unicode_minus'] = False

Latex : use unicode minus sign

If you prefer to use the minus sign instead of the hyphen, you can add this in the preamble of your Latex document:

\usepackage[utf8]{inputenc}
\DeclareUnicodeCharacter{2212}{$-$}

Latex should then recognize the character U+2212 and express correctly the negative numbers with a minus sign. Below is the output I get with Latex with hypens (top) and with minus signs (bottom):