this answer by @mdboom might help...
https://stackoverflow.com/a/16345065

And setting the default body text in TeX does not (by default) change the math font. This is (unfortunately standard TeX behavior).

The solution I use when I want all sans-serif out of TeX is to use the cmbright package, which can be turned on by adding:

rc('text.latex', preamble=r'\usepackage{cmbright}')

Using that suggestion, here are the results...

BEFORE

AFTER

That makes sense to me. OTOH, we maybe could do a better job of documenting this. I don't think its trivial for a user to know that they need to setup TeX by hand this way.

Possibly more info at?

https://matplotlib.org/tutorials/text/usetex.html

I am trying to come up with a good documentation entry for this. Found 3 other issues that have the same root cause (i.e. not knowing that changing text font in TeX doesn't automatically change the math font) -- #8436, #6041, #3999.

I think an entry that says “font selection using tex” or some such would be helpful. Show changing the basic font and the math font.

Long term I really wonder if the Tex rendering should not consult the non-Tex font selection mechanisms at all, and users should set the preamble by hand to get what they want. That would reduce confusion in my mind.

As commented here, one can turn the use of tex off for the ScalarFormatter such that the set font is used for the labels as well.

 ax.xaxis.get_major_formatter()._usetex = False
 ax.yaxis.get_major_formatter()._usetex = False

but then the tick labels won't be rendered using TeX (and other mathematical symbols, numbers will still be using TeX when text.usetex=True) which is inconsistent. When the user sets text.usetex = True the expected result is that all the fonts will be rendered using TeX. Hence, it would be better to ask the user to control the font by using text.latex.preamble.

The ticklabels do use tex, because text.usetex=True is set. But they are not rendered in math mode (i.e. the $ are removed). Hence they use the same font used by the rest of the document, but still through the tex system in use.

ahh right... that makes sense. But, this won't solve the issue if you have a mathematical formula in the title (or annotations) since it has to be rendered in math mode.

usetex_maths_DejaVu-Sans.png

usetex_maths_cmbright.png

In this issue, there is no math mode text used. Hence this would solve this issue.

In theory I think we could emit something along the lines of \everymath\expandafter{\the\everymath\sf} in the TeX preamble in such cases, which would have the effect of defaulting TeX math to sans-serif.
However, note that the default font.family is already sans-serif (that's why plain text (not math) defaults to a sans-serif font in Matplotlib), so this would effectively affect nearly anyone who is using usetex, even though most users likely associate usetex with the default Computer Modern Roman font (both from classical TeX behavior and from longstanding Matplotlib behavior). So I guess the question is, is it worth making a breaking change here?

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