Side-by-side equations using minipage have offset

Question

Using minipage to have side-by-side equations seems to give them an offset when one of them contains a fraction:

Code here:

\vspace{0.5cm}
\begin{minipage}{.5\linewidth}
    \begin{equation}
    \alpha (u,v) = \frac{N\!A}{n_s \sqrt{1 - \left(\frac{N\!A \rho}{n_s}\right)^2}}
    \label{eq:alpha}
    \end{equation}
\end{minipage}
\begin{minipage}{.5\linewidth}
    \begin{equation}
    d = \alpha \rho z
    \label{eq:disparity}
    \end{equation}
\end{minipage}
\vspace{0.5cm}

Any idea how to fix this? or a better way to achieve the same results sans offset?

Welcome to TeX SX! minipages are vertically centred by default. Try \begin{minipage}[t] — Bernard, Jun 18 '20 at 17:13

David Carlisle · Answer 1 · 2020-06-20T09:04:12.863

Posted for Barbara who is having computer issues.

@Bernard has provided the canonical reason for the misalignment: minipages are vertically centered by default. But the suggestion for correcting the alignment, using the option [t], doesn't have the desired effect; the second equation is now just a bit higher than the first.

@egreg has produced the desired result, along with a differently formulated reason for the misalignment. But there is a more compact way to get this result as long as you understand the reason for the misalignment and the way that (La)TeX measures the height and depth of a math expression. The \vphantom need contain just the elements of the "taller" expression; it's not necessary to set the whole thing twice. And if one of the equations is taller on the top and the other one deeper on the bottom, a minimal \vphantom can be applied as necessary to each, to even out the height and depth. (That is left as an exercise to the reader.)

\documentclass{article}
\begin{document}
\thispagestyle{empty}
Using a \verb+\vphantom+:
\noindent
\begin{minipage}{.5\linewidth}
    \begin{equation}
    \alpha (u,v)
       = \frac{N!A}{n_s \sqrt{1 - \left(\frac{N!A \rho}{n_s}\right)^2}}
    \label{eq:alpha}
    \end{equation}
\end{minipage}%
\begin{minipage}{.5\linewidth}
    \begin{equation}
    d = \alpha \rho z
       \vphantom{\frac{N}{\sqrt{\left(\frac{N}{n_s}^2\right)}}}
    \label{eq:disparity}
    \end{equation}
\end{minipage}
\bigskip
using the optional \verb+[t]+ for top alignment:
\noindent
\begin{minipage}[t]{.5\linewidth}
    \begin{equation}
    \alpha (u,v)
       = \frac{N!A}{n_s \sqrt{1 - \left(\frac{N!A \rho}{n_s}\right)^2}}
    \end{equation}
\end{minipage}%
\begin{minipage}[t]{.5\linewidth}
    \begin{equation}
    d = \alpha \rho z
    \end{equation}
\end{minipage}
\end{document}

Thanks! Where does \verb come into it? Not sure if I'm missing something - egreg's method works for me while yours doesn't seem to. — ajsc4, Jun 20 '20 at 08:54
@ajsc4 Barbara just used verb in the documentation to make [t] it isn't used in the code — David Carlisle, Jun 20 '20 at 09:03

score 1 · Accepted Answer · answered Jun 18 '20 at 17:30

You need to ensure that the two objects have the same height (and depth). The simplest is to typeset each equation twice, one for output and one as a vertical phantom.

In the phantom I disable \label, so it won't be seen.

The optional argument is the fraction of space to reserve for the left equation.

\documentclass{article}
\usepackage{amsmath}
\usepackage{lipsum} % just for the example
\newcommand{\sidebysideequations}[3][0.5]{%
  \begin{equation}
  \begin{minipage}{#1\displaywidth}%
  \begin{equation}\vphantom{\def\label##1{}#3}#2\end{equation}
  \end{minipage}
  \begin{minipage}{\dimexpr\displaywidth-#1\displaywidth}
  \begin{equation}\vphantom{\def\label##1{}#2}#3\end{equation}
  \end{minipage}
  \end{equation}
}
\begin{document}
References: \eqref{eq:alpha}, \eqref{eq:disparity}
\lipsum[1][1-5]
\sidebysideequations[0.6]{
    \alpha (u,v) = \frac{N!A}{n_s \sqrt{1 - \left(\frac{N!A \rho}{n_s}\right)^2}}
    \label{eq:alpha}
}{
    d = \alpha \rho z
    \label{eq:disparity}
}
\lipsum[2][1-5]
\end{document}

That works, thanks! Only issue is that the left-hand equation seems to have an extra indent - it's positioned further right than when using 'vanilla' minipage — ajsc4, Jun 20 '20 at 08:57
@ajsc4 Optical illusion due to the minipage on the left being wider than the one on the right. — egreg, Jun 20 '20 at 11:34

score 1 · Answer 3 · answered Jun 18 '20 at 20:13

We need to set common baseline of two outputs of display math. This can be done by \unskip\unpenalty in \vbox just after the display math is closed and paragraph is finished:

\def\twodisplays#1#2{\vbox{\hsize=.5\hsize$$#1$$\par\unskip\unpenalty}%
                     \vbox{\hsize=.5\hsize$$#2$$\par\unskip\unpenalty}}
Test:
$$\twodisplays
  {
    \alpha (u,v) = {N!A \over n_s \sqrt{1 - \left( N!A \rho \over n_s\right)^2}}
    \eqno (1)
  }
  {
    d = \alpha \rho z
    \eqno (2)

  }
$$
next text.

Side-by-side equations using minipage have offset

3 Answers3

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