"evaluated at" vertical bar

[Peter Cao]

Question's already been asked ahead of me, with no answer, in another
forum so to quote somebody else:

I'm typing a document in the typsetting language LaTeX. How do I make
a vertical bar next to a derivative fraction that means "evaluate at"?
I want to write something like \frac{df}{dx} |_{x=0}, but this (and
vert) makes the vertical bar much too short. I think the vertical bar
is supposed to be as tall as the fraction. \right | would make it the
right size, but I need a matching \left |, and I don't want that.

thanks



Now I looked it up, and the only solution is to use \bigg| Big| but
these doesn't automatically scale to the full height of the line and I
just want a reliable solution without too much cerebral intervention
and fidgetting about on my part. Suggestions?

[Davide P. Cervone]

Use \left. to match a \right but produce no output. So

\left. \frac{df}{dx} \right|_{x=0}

should work for you.

Davide

[Peter Cao]

Yes, exactly what I needed; thanks again Davide.

> > and fidgetting about on my part.  Suggestions?- Hide quoted text -
>
> - Show quoted text -