Let pgf backend use bracket delimiters for detecting math mode. #23381

painch · 2022-07-02T00:12:41Z

PR Summary

LaTeX (and lualatex/xelatex) allows math mode to be delimited by '$', '$', '\[' and '\]'. This PR changes the pgf backend to detect this, so that e.g. '_' and '^' are not inadvertently escaped in math-mode labels etc.

The current behaviour leads to errors when certain label names are used. For example I've put a minimum working example script mwe.py and a tex file mwe.tex below. Running mwe.py show allows the use of non-pgf backends (Qt5Agg in my case), and displays $x^2$ as $x^2$ correctly, whereas using just plain mwe.py then lualatex mwe.tex shows it as $x2$. This PR fixes this issue.

mwe.py:

#!/usr/bin/env python3

import sys
import matplotlib.pyplot as plt

plt.plot([0,1,2],[0,1,4])
plt.xlabel(r'\(x\)')
plt.ylabel(r'\(x^2\)')

if len(sys.argv)>1 and sys.argv[1]=='show':
    plt.show()
else:
    plt.savefig('mwe.pgf')

mwe.tex:

\documentclass{standalone}
\usepackage{pgf}

\begin{document}
\input{mwe.pgf}
\end{document}

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oscargus · 2022-07-04T08:52:12Z

I think that this probably makes sense, but please include a test for it. I think something like this could be used as a template:

matplotlib/lib/matplotlib/tests/test_backend_pgf.py

Lines 326 to 334 in cd9d371

    
           @check_figures_equal(extensions=["pdf"]) 
        
           @pytest.mark.parametrize("texsystem", ("pdflatex", "xelatex", "lualatex")) 
        
           @pytest.mark.backend("pgf") 
        
           def test_minus_signs_with_tex(fig_test, fig_ref, texsystem): 
        
               if not _check_for_pgf(texsystem): 
        
                   pytest.skip(texsystem + ' + pgf is required') 
        
               mpl.rcParams["pgf.texsystem"] = texsystem 
        
               fig_test.text(.5, .5, "$-1$") 
        
               fig_ref.text(.5, .5, "$\N{MINUS SIGN}1$")

Use $ for the reference and the new delimiters for the test.

For me, this still works correctly in the non-TeX backends with text.usetex=True, with or without this change. (And it doesn't work using the mathtext backend with or without it.)

timhoffm · 2022-07-04T10:51:46Z

I'm hesitant with this inclusion. As far as I understand LaTeX:

\[...\] is display math mode, which puts the equation on a dedicated line. - Matplotlib's math mode does not support this. Therefore, I think we should not accept this syntax.
$...$ is equivalent to $...$ . So one could argue that we should support this as well. Note however, that due to the asymmetry/symmetry of the delimiters, the matching algorithm would need to be different. $...$ just identifies pairs. However, you cannot simply add $ and $ to the matching regexp, because you would also incorrectly match The \) inverted $ brackets or even mixtures $ between $ syntaxes.
Getting this right is significant work. I therefore propose not to support $...$ and instead explicitly document that.

…ed).

painch · 2022-07-04T17:55:30Z

* `\[...\]` is display math mode, which puts the equation on a dedicated line. -  Matplotlib's math mode does not support this. Therefore, I think we should not accept this syntax.

That is a good point -- I've now made a change to reflect that.

* `\(...\)` is equivalent to `$...$`. So one could argue that we should support this as well. Note however, that due to the asymmetry/symmetry of the delimiters, the matching algorithm would need to be different. `$...$` just identifies pairs. However, you cannot simply add `\(` and `\)` to the matching regexp, because you would also incorrectly match `The \) inverted \( brackets` or even `mixtures $ between \) syntaxes`.

At least in their TeX Live implementations, lualatex, pdflatex and xelatex don't allow nested $...\(...$...\), but do allow mixed $...$ and $...$, so the matching algorithm should still work on any valid input, without any major changes.

  Getting this right is significant work. I therefore propose not to support `\(...\)` and instead explicitly document that.

That is a very reasonable alternative if this doesn't work out.

timhoffm · 2022-07-06T22:08:58Z

lualatex, pdflatex and xelatex [...] do allow mixed $...$ and $...$

Do the they allow \)...\(?

painch · 2022-07-13T21:23:19Z

lualatex, pdflatex and xelatex [...] do allow mixed $...$ and $...$

Do the they allow \)...\(?

They don't

painch · 2022-07-13T22:42:04Z

I think that this probably makes sense, but please include a test for it. I think something like this could be used as a template:

I've had a go writing tests (see the last commit to this branch), I've tried them out locally, though I'm unfamiliar with pytest so they might need some checking.

anntzer · 2022-07-13T22:51:09Z

It would seem like a more robust(?) solution may be to just completely get rid of _tex_escape and instead configure tex to support _^% in text mode (I'm not really sure we can do anything, or if the current code does anything, about $?). For underscores this is already done in standard usetex via the underscore latex package, and my uneducated guess is that we can implement something similar for ^ and %

melissawm · 2023-01-22T21:40:14Z

Hi @painch - let us know if you need any guidance on moving this forward. Thanks!

anntzer · 2023-01-22T22:01:44Z

I think this is superseded by #23442.

jklymak · 2023-01-26T02:51:07Z

Let's close in favour of #23442 and lack of response. @painch Thanks for your contribution - it definitely inspired an improvement!

github-actions bot reviewed Jul 2, 2022

View reviewed changes

oscargus added topic: text/mathtext backend: pgf status: needs tests and removed topic: text/mathtext labels Jul 4, 2022

Let pgf backend use bracket delimiters for detecting math mode (rebas…

2588b1d

…ed).

painch force-pushed the main branch from 67c6ecd to 2588b1d Compare July 4, 2022 17:42

Callum Watson added 2 commits July 13, 2022 23:38

Let pgf backend use bracket delimiters for detecting math mode

d8a40c9

Add tests for letting pgf backend use bracket delimiters

1b96418

This was referenced Jul 14, 2022

Tweak pgf escapes. #23427

Merged

Remove need to detect math mode in pgf strings #23442

Merged

github-actions bot added the status: needs rebase label Oct 18, 2022

jklymak closed this Jan 26, 2023

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Let pgf backend use bracket delimiters for detecting math mode. #23381

Let pgf backend use bracket delimiters for detecting math mode. #23381

painch commented Jul 2, 2022

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oscargus commented Jul 4, 2022

timhoffm commented Jul 4, 2022 •

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painch commented Jul 4, 2022

timhoffm commented Jul 6, 2022

painch commented Jul 13, 2022

painch commented Jul 13, 2022

anntzer commented Jul 13, 2022

melissawm commented Jan 22, 2023

anntzer commented Jan 22, 2023

jklymak commented Jan 26, 2023

Let pgf backend use bracket delimiters for detecting math mode. #23381

Let pgf backend use bracket delimiters for detecting math mode. #23381

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painch commented Jul 2, 2022

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timhoffm commented Jul 6, 2022

painch commented Jul 13, 2022

painch commented Jul 13, 2022

anntzer commented Jul 13, 2022

melissawm commented Jan 22, 2023

anntzer commented Jan 22, 2023

jklymak commented Jan 26, 2023

timhoffm commented Jul 4, 2022 •

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