# How can I vertically align the numerators of two fractions?

I am writing the following formula:

% arara: lualatex

\documentclass{article}
\usepackage{mathtools}
\usepackage{unicode-math}

\begin{document}
$y_\mathup{COG}=\frac{h}{3}\frac{l_\mathup{c,a}+2l_\mathup{c,i}}{l_\mathup{c,a}+l_\mathup{c,i}}$
\end{document}


which yields: I don't like the way, the h and l_\mathup{index} is vertically aligned. Is that typical behavior? Good style? Could I avoid that?

You can trick LaTeX into thinking the h had a subscript and thereby moving it upward to align with the l.

Alternatively, you can \smash the subscripts or the ls and thus lower them (this might look a bit cramped if you compare the space above and below the fraction bar).

\documentclass{article}
\usepackage{mathtools}
\usepackage{unicode-math}

\begin{document}
\begin{centering}
no modification
$\enskip y_\mathup{COG}=\frac{h}{3}\frac{l_{\mathup{c,a}}+2l_\mathup{c,i}}{l_\mathup{c,a}+l_\mathup{c,i}}$
\verb|\vphantom|
$\enskip y_\mathup{COG}=\frac{h_{\vphantom{\mathup{c,a}}}}{3}\frac{l_{\mathup{c,a}}+2l_\mathup{c,i}}{l_\mathup{c,a}+l_\mathup{c,i}}$
\verb|\smash|
$\enskip y_\mathup{COG}=\frac{h}{3}\frac{l_{\smash{\mathup{c,a}}}+2l_{\smash{\mathup{c,i}}}}{l_{\smash{\mathup{c,a}}}+l_{\smash{\mathup{c,i}}}}$
\end{centering}
$\enskip y_\mathup{COG}=\frac{h}{3}\frac{l+2l}{l+l}$
\end{document} This behaviour seems to be caused by unicode-math, if compiled without that package the h and l are properly aligned without any modifications, indeed the modifications do not even seem to have an effect.

• I wouldn't call this method a "trick". The \vphantom instruction was created on purpose to let users insert "struts" -- items that have height and/or depth but no width and hence are invisible -- to modify the heights and depths of the "boxes" that are TeX's most basic typeset items. – Mico Sep 10 '13 at 10:10
• I mark this as an answer because it solves the problem. Thanks. The real answer, however, seems to be, that unicode-math has a bug. Without it, everything looks beautiful (like your \vphantom solution). – LaRiFaRi Sep 10 '13 at 10:32
• github.com/wspr/unicode-math/issues/259 says, it is not a bug. I've added the vphantoms now. – LaRiFaRi Sep 10 '13 at 12:18

No, it's not typical behavior or good style (to my taste, at least). You won't have it, for instance, if you don't use the mathtools package:

\documentclass{article}

\begin{document}
$y_{COG}=\frac{h}{3}\frac{l_{c,a}+2l_{c,i}}{l_{c,a}+l_{c,i}}$
\end{document}


I don't have the package installed, so I cannot easily tell you if it's your doing or a bug. One thing is certain, though, I think you need to add your \mathup subscripts in extra braces, like this:

\documentclass{article}
\usepackage{mathtools}
\usepackage{unicode-math}

\begin{document}
$y_{\mathup{COG}} = \frac{h}{3} \frac{l_{\mathup{c,a}}+2l_{\mathup{c,i}}} {l_{\mathup{c,a}}+l_{\mathup{c,i}}}$
\end{document}


This could be the source of your problem.

• Thank you. Actually the bug is in unicode-math. Mathtools works fine. I replaced unicode-math by amssymb and that works also. I will report that. Your second remark: the braces don't change anything. They are redundant. – LaRiFaRi Sep 10 '13 at 10:30