# How to display compound fractions with subscripts correctly?

Which is the correct way to represent a compound fraction in an equation environment? With correct I mean, a way so that the representation would give the same font dimension for all the numerators and denominators. Consider the following image:

I would like, for example, that w_{VDW} would have the same dimension as of H_{W,VDW}. Is this the typographically correct choice? What would you suggest?

I have tried \sfrac but it seemed worse.

• Have you read Fractions with large elements? The \ddfrac macro may be what you're looking for. – Mico Jun 8 '16 at 16:06
• @Mico: thanks for the suggestion. I'll check it. – Andrea Jun 8 '16 at 16:10
• personally I'd let the numerator and denominator be smaller but it's your choice but Mico's answer in the referenced question should produce what you want. – David Carlisle Jun 8 '16 at 16:11
• @Mico: your suggestion produces the requested result. Thank you! – Andrea Jun 8 '16 at 16:17
• Without amsmath (and \dfrac), one can always use the \displaystyle\frac{}{} syntax. – Steven B. Segletes Jun 8 '16 at 16:19

It's mainly a question of style. I'll give you three different strategies.

\documentclass{article}
\usepackage{amsmath}
\begin{document}

First display with \verb|\frac|, in the right hand side
the fractions are smaller
$\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \frac{\Delta_{VDW}}{w_{VDW}} }{ \frac{\Delta_{TDW}}{w_{TDW}} }$
and second display with \verb|\dfrac|, in the right
hand side the fractions are larger
$\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \,\dfrac{\Delta_{VDW}}{w_{VDW}\mathstrut}\, }{ \,\dfrac{\mathstrut \Delta_{TDW}}{w_{TDW}}\, }$
Finally, a third display with the slashed form
$\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \Delta_{VDW}/w_{VDW} }{ \Delta_{TDW}/w_{TDW} }$
\end{document}


And a fourth display, with the \mfrac (~80 % of \displaystyle) from nccmath. Picking up egreg's example:

\documentclass{article}
\usepackage{nccmath}

\begin{document}

First display with \verb|\frac|, in the right hand side
the fractions are smaller: $\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \frac{\Delta_{VDW}}{w_{VDW}} }{ \frac{\Delta_{TDW}}{w_{TDW}} }$
and second display with \verb|\dfrac|, in the right
hand side the fractions are larger: $\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \,\dfrac{\Delta_{VDW}}{w_{VDW}\mathstrut}\, }{ \,\dfrac{\mathstrut \Delta_{TDW}}{w_{TDW}}\, }$
Finally, a third display with \verb|\mfrac| in the right-hand side as a compromise: $\frac{H_{W,WDV}}{H_{W,TDW}}= \frac{ \,\mfrac{\Delta_{VDW}}{w_{VDW}\mathstrut}\, }{ \,\mfrac{\mathstrut \Delta_{TDW}}{w_{TDW}}\, }$ \end{document}