Math formulas displaying oddly

[PCZatDalton]

Mathematical formulas in the form of <numeral>x-<numeral> don't display properly in posts. The x becomes small and superscripted. When included in a LaTeX block, it causes the formula to be unrenderable.

For example: 2x-1 and $latex 2x-1 $ both exhibit this bug.

Confirmed in 4.0 and 4.0.1, with a fresh installation and no plugins, and the default theme.

[nacin]

How do you use LaTeX in your posts? With a shortcode from a plugin?

[PCZatDalton]

Replying to nacin:

How do you use LaTeX in your posts? With a shortcode from a plugin?

We're using the WP Latex plugin like so: $latex <theformula>$

However, the problem crops up even when writing straight text w/o passing it through LaTeX. But when we do render it with LaTeX, it causes the rendering to fail.

[miqrogroove]

Example page? Screenshot? Any other helpful info?

[miqrogroove]

Found the patch here:

​https://plugins.trac.wordpress.org/changeset/982453/

You will need to contact the plugin author about getting that next version released so that it will be an easy update.

[PCZatDalton]

Replying to miqrogroove:

Example page? Screenshot? Any other helpful info?

It's extremely easy to reproduce. Just type, for example, "2x-1" into a post. See what happens to the x? Now type "$latex 2x-1$" into a post. See how it doesn't render?

Changing the "x" to, say, a "y" doesn't exhibit the problem. Nor does changing the minus to a plus or putting a space between the "x" and the minus sign. See the examples in the screen shot, below:

Note that once the problem was noticed on our school blog, I made a new installation of WP on my testing server, and the problem persists there. I didn't install WP Latex or test LaTeX rendering on that test server, however, because the plain jane installation already exhibited the weird behavior wherein it changed the x to a small raised x--and this seems to be the problem that's interfering with the LaTeX rendering.

[miqrogroove]

Please contact the plugin author about this.

[PCZatDalton]

Replying to miqrogroove:

Please contact the plugin author about this.

Miqrogroove-

I'm sorry to be rude about this, but you're clearly not reading my comments. The problem PRECEDES the WP Latex plugin. It's a problem in the core, that renders incorrectly in the core, and causes a fatal error in the WP Latex plugin.

This is a problem for our math teachers, whether or not they use Latex, so please stop marking this case closed. It is not. Ok?

[rmccue]

Hi PCZatDalton, thanks for the bug report here.

Here's what seems to be happening with the issue. wptexturize takes care of changing certain characters, such as -- to an en dash. One of the things it handles here is changing the `x` in 9x9 to a real multiplication symbol. (For example, something like 1024x768)

This was changed in r28719 (#19308) to also include negative numbers, but it looks like it might be an issue, since x is also a valid variable name. While the LaTeX plugin could be fixing this, it'd really be a workaround.

I'd suggest we remove the - from the regex, so that it only matches 9x9 not also 9x-9, which is ambiguous.

[miqrogroove]

PCZatDalton, I suggest installing the Jetpack version of latex. While rmccue is correct that we could hack the core code to change the behavior of minus signs, it would not fix the underlying bug in the plugin.

[PCZatDalton]

Replying to miqrogroove:

PCZatDalton, I suggest installing the Jetpack version of latex. While rmccue is correct that we could hack the core code to change the behavior of minus signs, it would not fix the underlying bug in the plugin.

The problem is, as rmccue points out, that wptexturize is overly aggressive. This means that, even if the formula is not processed as LaTeX, it still displays incorrectly.

Our use case is such that this behavior (turning 'x' into the multiplication symbol) is rarely, if ever, desired--but I can see how others may see it as the more common approach. If the consensus opinion is that it is currently behaving correctly, then I'll suggest to the WP Latex maintainers to implement the patch that you found, and I'll tell my math teachers to update their usage accordingly.

[rmccue]

Replying to miqrogroove:

While rmccue is correct that we could hack the core code to change the behavior of minus signs, it would not fix the underlying bug in the plugin.

The plugin should be updated to run before texturize for sure, but the core behaviour here is absolutely wrong, and we should fix it regardless. :)

[helen]

We're on the late side for addressing this in 4.1, let's get a patch going here and do 4.2.

[nacin]

This is a 4.0 regression and would be an easy regex fix, so bringing this back to 4.1.

[rmccue]

Change regex to not include -

[rmccue]

Include unit tests

[rmccue]

Added patch and tests.

[miqrogroove]

Patch looks good.

The allowance for negative signs came from a 3-year-old patch at https://core.trac.wordpress.org/attachment/ticket/19308/19308.patch and it wasn't considered a regression until now.

[markjaquith]

Bot failure?

In [30752]:

Revert [28719] and no longer math-process multiplication of negative numbers
see #19308
fixes #30445
props rmccue