LaTeX / MathJax rendering bugs

[avm19]

Just a week or two ago this text would have rendered correctly in discussions, issues, PR messages etc:
Bla $\sum_j j$ but $\sum_j$
At the time of writing, it looks like that:

Here is how it is being rendered when you are reading this message:
Bla $\sum_j j$ but $\sum_j$
Here is what it supposed to look like (rendered at stackexchange.com):

Here are related discussions 3-4 weeks ago:
#16939
#17384

I emphasise that certainly two weeks ago (and probably also 1 week ago) this bug did not occur (in case you are interested, here is the message, which I remember to have looked fine). You must have pushed some buggy changes to the rendering algorithm within this time period.

---

Update

This issue is known to the support, here is the answer I received after submitting a bug report through the link kindly suggested in the messages below.

Hi avm19,

Thanks for reaching out to GitHub Support about problems rendering multiple inline math statements in a line. We have received some reports of this and our team is currently working on a fix for this. I have added your report to the internal issue where this is being tracked and we will follow-up with you when this has been fixed.

Note that while this support ticket may automatically close, that the internal issue will remain open and under investigation.

Thanks,

Update-2. @nschloe suggested the following workaround:

• for inline formulae, use $` <your_LaTeX> `$
• for displayed formulae, use ```math <your_LaTeX> ```

Test for the minimal example ${x}_{a} {y}_{b}$, which does not render correctly: ${x}{a} {y}{b}$

• [+] inline dollar-backtick-escaped: ${x}_{a} {y}_{b}$
• [+] displayed math code:

$${x}_{a} {y}_{b}$$

[DLu]

I have also encountered this. Here is my example

[ylamidon]

Same problem. My example

A workaround is to go the next line before $\delta$. A workaround

[avm19]

This is very clever to use linebreaks to break Markdown contexts that overarch multiple LaTeX formulas!

Unfortunately, it works well only in markdown file renders, but not in messages (like this one), since single linebreaks are not ignored here.

[MathiasReker]

Hello. You can report the bug here: https://support.github.com/contact/bug-report

[avm19]

Thanks. I couldn't find this link at all when navigating the website.

[avm19]

This issue is known to the support. I included their response in the head message.

[cloudy-sfu]

Here is my example: #20154

[DLu]

I believe this is fixed now

Bla $\sum_j j$ but $\sum_j$

[avm19]

True.

Update: see mbaudin47's comment.

[mbaudin47]

I do not think that this is fixed.

The equation $\boldsymbol{x}_0$ is OK,

but ${\boldsymbol{x}1, ..., \boldsymbol{x}{i-1}, \boldsymbol{x}_{i+1}, ..., \boldsymbol{x}_n}$ is not.

[avm19]

True. ${x}_{a} {y}_{b}$ would be close to the minimal example that fails. At the same time, ${x}_a {y}_b$ works: ${x}_a {y}_b$. A temporary dirty fix would be escaping underscores, as in ${x}\_{a} {y}\_{b}$ (${x}_{a} {y}_{b}$), which is wrong because one should not and would not escape those underscores in LaTeX.

[nschloe]

Recommendation: Avoid $-math, always use

$`a+b`$

```math
x+y
```

This avoids most issues, such as this one:

$`{\boldsymbol{x}_1, ..., \boldsymbol{x}_{i-1}, \boldsymbol{x}_{i+1}, ..., \boldsymbol{x}_n}`$

${\boldsymbol{x}_1, ..., \boldsymbol{x}_{i-1}, \boldsymbol{x}_{i+1}, ..., \boldsymbol{x}_n}$

[avm19]

@nschloe Nice! Although you can't avoid $-math if you want an inline formula (can you?), you can add backticks to mess with GitHub's markdown translator, so that it produces the desired result. That is,

• for displayed formulae, use ```math <your_LaTeX> ```
• for inline formulae, use $` <your_LaTeX> `$

Test:

• [-] minimal example of the bug (doesn't render right): ${x}{a} {y}{b}$
• [+] inline dollar-backtick-escaped: ${x}_{a} {y}_{b}$
• [+] displayed math code:

$${x}_{a} {y}_{b}$$

P.S. I don't know what ` is used in LaTeX, so this trick should be okay.

[nschloe]

$-math if you want an inline formula (can you?), you can add backticks

That's what I mean: $-math is without backticks, $`-math with. Always use the latter. (I consider it a mistake that GitHub ever allowed using $-math, it complicates things a lot.)

PS: See https://github.com/nschloe/github-math-bugs/ for a list of current math bugs.