Overfull hbox when using subequations and empheq inside a minipage

[profjoaoalvesjr]

I got 8 warnings of bad boxes, "Overfull \hbox (1.66663pt too wide)", when I compile the following code. When I use align instead of empheq, the bad boxes don't occur.

\documentclass[10pt, aspectratio=169]{beamer}
\usetheme{Berkeley}
\usepackage{empheq}

\begin{document}

\begin{frame}
\frametitle{Rotations in the plane}
\begin{minipage}[c]{0.34\textwidth}
\begin{figure}[H]
  \text{(FIGURE HERE)}\\
  \hspace{115pt}
\end{figure}  
\end{minipage}\hfill
\begin{minipage}[c]{0.64\textwidth}
  \begin{itemize}
    \item In an orthogonal coordinate system \( Oxy \), rotating a point \( P = (x, y) \) by an angle \( \theta \) around the origin, with \( r = \sqrt{x^2 + y^2} \), \( x = r \cos \alpha \), and \( y = r \sin \alpha \), results in the point \( P' = (x', y') \) such that
        \[  \begin{aligned}
              x' &= r\cos(\alpha+\theta) = r \cos \alpha \cos \theta - r \sin \alpha \sin \theta,\\
              y' &= r\sin(\alpha+\theta) = r \sin \alpha \cos \theta + r \sin \theta \cos \alpha;\\
            \end{aligned}\]
        that is,
        \begin{subequations}
        \label{E:RotPlanCoordOrt}
          \begin{empheq}[left=\empheqlbrace\,]{align}
            x' &= x \cos \theta - y \sin \theta, \label{E:RotPlanCoordOrtox}\\
            y' &= x \sin \theta + y \cos \theta. \label{E:RotPlanCoordOrtoy}
          \end{empheq}
        \end{subequations}
  \end{itemize}
\end{minipage}
\end{frame}

\end{document}

[daleif]

Always make the example as small as possible.

This gives the same warnings. I'll have a look

\documentclass[10pt]{beamer}
\usepackage{empheq}
\begin{document}
\begin{frame}
  \begin{empheq}[left=\empheqlbrace\,]{align}
    x' &= x \cos \theta - y \sin \theta, \label{E:RotPlanCoordOrtox}\\
    y' &= x \sin \theta + y \cos \theta. \label{E:RotPlanCoordOrtoy}
  \end{empheq}
\end{frame}
\end{document}

Additionally, this does not give the warnings

%\documentclass[10pt]{beamer}
\documentclass[10pt]{article}
\usepackage{empheq}
\begin{document}
%\begin{frame}
  \begin{empheq}[left=\empheqlbrace\,]{align}
    x' &= x \cos \theta - y \sin \theta, \label{E:RotPlanCoordOrtox}\\
    y' &= x \sin \theta + y \cos \theta. \label{E:RotPlanCoordOrtoy}
  \end{empheq}
%\end{frame}
\end{document}

So it seems beamer is relevant.

[muzimuzhi]

Also the bad box only appears when a empheq-defined delimiter is used (like in left=\empheqlbrace) and the equation has tag(s).

Then inside \empheqlbrace, somehow the \EQ_tag_box was wider than .5\maxdimen, thus the overfull hbox warning in the use of \parbox{.5\maxdimen}{... \usebox{\EQ_tag_box} ...}.

Update: \EQ_tag_box is set by \EQ_typeset_tags: so the overfull hbox is also raised there.

mathtools/empheq.dtx

Lines 3492 to 3502 in 23e4b51

	\def\EQ_declare_left_delimiter:nnnn #1#2#3#4{%
	\@namedef{empheq#3\expandafter\@gobble\string#2}{%
	\left#2%
	\mkern-\thinmuskip
	\vphantom{#4{\parbox{.5\maxdimen}{%
	\EQ_predisplay_adjustment:
	\EQ_prevent_vertical_space:
	\usebox{\EQ_tag_box}%
	\EQ_postdisplay_adjustment:}}}%
	\right.%
	\kern-\nulldelimiterspace #1}}

[daleif]

@muzimuzhi it seems to also be only when \label is used.

[muzimuzhi]

@daleif True.

Also the amount of overfull is the current value of \thinmuskip in pt. Change \thinmuskip and the overfull amount changes accordingly.

Running the example in #63 (comment) on overleaf.com, overfull hbox is reproducible in as early as texlive 2014.