[texhax] Appropriate way to add multiline (explanatory) text to an equation?

[Morten Høgholm]

On Mon, 07 Jun 2004 13:47:30 +0100, Chris Rowley <C.A.Rowley at open.ac.uk>  
wrote:

> William
>
>> > why not use a \parbox, or isn't that permitted in math?
>>
>> Hmm, that does work in math. Okay, it's good except that it wants a
>> size up-front... guess I'll need to calculate that.
>>

This is dirty but might do the job:

\documentclass{article}
\usepackage{empheq} % v2.0
\EmphEqInternalSyntaxOn
\def\EmphEqdisplaywidth{\l_empheq_displaywidth_dim}
\EmphEqInternalSyntaxOff
\begin{document}
\hrule
\begin{empheq}[
   left={\parbox[c][\EmphEqdisplayheight+\EmphEqdisplaydepth][t]
          {\linewidth-\EmphEqdisplaywidth-6cm}
          {Text spanning multiple lines}\quad}]
     {align}
   a&=\int_0^1 x\,dx +\frac{foo + bar}{baz}\\
   E&= mc^2
\end{empheq}
\end{document}

You might want to add an \fbox around \parbox for illustration purposes.

> At present (as far as I know) most extras related to display math need
> thought about sizing and positioning.  It would be interesting to see
> some precise specs for things that should not be like that.

Yes, those two are a pain. It took me serious trouble to get empheq to  
work properly (I more or less think it does so now).

> The more general idea is, I think, of a \parbox/minipage (or an LR
> box?) where
>   `the internal text width is set to some precalculated
>    value based on the position of the `box' '.

Maybe one could utilize \pdflastxpos et al. for this?

> And this is perhaps getting towards `the limits of TeX'; so there's a
> challenging problem for someone's summer vacation!

Sigh! Another one. My summer vacation is looking packed -- at this rate I  
might not even have time for my girlfriend... Foolish how I thought  
vacation was the time where I could relax. ;-)
-- 
Morten Høgholm