# Is there a way to produce an “evaluate at” vertical bar that resizes properly in display formulae?

There are two examples of what I am talking about in this equation: $$\displaystyle \left.\mathrm{d}\Phi\left(v\right)\right|_{p}\equiv\left.v^{\mu}\frac{\partial\Phi^{\lambda}}{\partial x^{\mu}}\frac{\partial}{\partial y^{\lambda}}\right|_{\Phi\left(p\right)}.$$

They are the vertical bars that inform the reader what value is used for evaluation of the preceding expressions.

When I try to produce such a result, the bar resizes inappropriately. I want this this for text and display equations, not form input. Is there a way to accomplish what I am asking for?

• Have you tried setting SpanMaxSize -> Infinity for the Cell you put the expression in? – Mr.Wizard Aug 13 '18 at 7:21
• Nope. I have that set globally. – Steven Thomas Hatton Aug 13 '18 at 7:32
• If, with that setting in place, I right click on the expression in your question here, select Show Math As > MathML Code, then copy that code and paste it into the Notebook, letting Mathematica interpret the result, I see basically the same expression. Do you also? – Mr.Wizard Aug 13 '18 at 7:53
• Yes, but it will take some time to figure out which part of the Cell expression makes it work. And then, how should it be input without jumping through hoops? – Steven Thomas Hatton Aug 13 '18 at 7:59
• I was not suggesting that was a solution itself, rather a proof that Mathematica can display the expression, and therefore this question should be answerable. I am not awake enough to give it a proper try however. – Mr.Wizard Aug 13 '18 at 8:01

Perhaps you can use an input alias? For example:

CurrentValue[EvaluationNotebook[], InputAliases] = {
"at" -> SubscriptBox[
RowBox[{
"\[SelectionPlaceholder]",
StyleBox["\[RightBracketingBar]", FontFamily->"Times"]
}],
"\[Placeholder]"
]
};


And here is an animation producing your desired formula:

(note that I modified the style sheet to adjust the ScriptLevel, FontSize and FontFamily of inline cells)