Triple and quadruple dot Mathtext accents don't stack or align.

[danzimmerman]

Issue

Triple and quadruple dots accents used above a quantity for higher-order time derivatives do not align the same way as single and double:

Code

plt.plot()
plt.gca().annotate(r'$\dot{\vec{q}}\hspace{1.5}\ddot{\vec{q}}\hspace{1.5}\dddot{\vec{q}}\hspace{1.5}\ddddot{\vec{q}}$', xy=(-0.025, 0))

Expected Outcome
The triple (\dddot{\vec{q}}) and quadruple (\ddddot{\vec{q}}) appear over the vector arrow like the single and double dots do

Actual Outcome
The triple and quadruple dots align to the left of the vector arrow:

Or whatever character is inside the brackets, here like \dddot{q}:

I notice in the documentation that \dddot and \ddddot are [not listed as accents]. Are they unsupported in mathtext?

As a partial workaround, I can adjust the horizontal alignment with negative \hspace and switch to bolded vector notation but can't find something to adjust it vertically if I want to use the vector arrow:

Version Info

• Operating system: Windows 11 Home Update 21H2
• Matplotlib version: 3.4.2 (conda-forge)
• Matplotlib backend: module://ipykernel.pylab.backend_inline
• Python version: 3.8.8
• Jupyter version (if applicable): Notebook version 6.3.0
• Other Jupyter versions:

jupyter                   1.0.0            py38haa244fe_6    conda-forge
jupyter_client            6.1.12             pyhd8ed1ab_0    conda-forge
jupyter_console           6.4.0              pyhd8ed1ab_0    conda-forge
jupyter_core              4.7.1            py38haa244fe_0    conda-forge
jupyterlab_pygments       0.1.2              pyh9f0ad1d_0    conda-forge
jupyterlab_widgets        1.0.0              pyhd8ed1ab_1    conda-forge

[jklymak]

If its easy to add them, you probably could have a go at it. I don't think those accents are heavily used, so there probably has not been demand to add them, versus any fundamental problem with them.

[QuLogic]

FWICT, the mapping to a glyph exists, but neither are in _accent_map, so they are not combined with any characters. There also don't appear to be any glyph definitions for combining versions of those characters, so I'm not sure just adding to _accent_map would work without font support.

[danzimmerman]

I'm not sure just adding to _accent_map would work without font support.

Seems to "work on my machine" in a basic way per the draft PR above but I don't know what else needs to happen to make sure it's fully supported in all relevant cases.

Does it also need entries in latex_to_standard in _mathtext_data.py?

[QuLogic]

Fixed by #20605, though there is an (unrelated) bug in the accent table, #20623.