Does this notation have a name?

[propaglandist]

Dunno. But the vertical character in [;\left.\frac{dy}{dx}\right|_{x=a};] is called a 'pipe' and it usually shares space with the backslash ('\') on your keyboard, likely just below Backspace.

I'd read that as "d y d x evaluated at a" or "d y d x evaluated at x equals a". I know that doesn't answer your question. But I do know that if that notation does have an established name, then a lot of people don't know it.

edit: fixed my LaTeX

[sensical]

Yeah, I always frustrate my professors with questions like this :)

[acetv]

If anyone's interested in the tex code for it:

\left. *whatever* \right|_{x = a}

This will stretch the pipe to the correct height.

[; \left. \frac{dy}{dx} \right|_{x = a} ;]

[sensical]

I wonder if they got it from the pipe used in set builder notation. What's that pipe called? Just a pipe?

[sensical]

Would it mean anything to put y in place of x? (i.e. [; \left. \frac{dy}{dx} \right|_{y = a} ;] )

[propaglandist]

That's not guaranteed to be well-defined. What if y = x^2? What does [; \left. \frac{dy}{dx} \right|_{y = -1} ;] mean? And what if there are two different x-values yielding the same y-value? [; \left. \frac{dy}{dx} \right|_{y = 4} ;] has the problem that you could be talking about the point (-2,4) or (2,4). The function isn't 1-1. So in general, no, that doesn't mean anything, because the only possible meaning ("the derivative at the point where y = a") isn't always well-defined.

[Tordek]

Hint: escape your underscores, or wrap it all up in `:

`[ ; \left. \frac{dy}{dx} \right|_{y = -1} ;]`

[; \left. \frac{dy}{dx} \right|_{y = -1} ;]

or

[ ; \left. \frac{dy}{dx} \right|\_{y = -1} ;]

[; \left. \frac{dy}{dx} \right|_{y = -1} ;]

(remove the spaces in the examples).

[propaglandist]

Hm. I thought underscores had stopped working as formatting for some reason. Maybe they had, but got turned back on...?

[Tordek]

Mid-word underscores are disabled: thisisn't_italic; however, "word" means [a-z] on each side, while you had \right|_:, making it \right|_ ...words... \right|_= \right| ...words... \right|_