Side to side subequations with minipages, but no textwidth setting gives satisfactory result

Question

\documentclass[a4paper, 12pt,twoside=on, listof=totoc, bibliography=totoc,]{scrreprt}

\usepackage{stackengine}
\usepackage{braket}
\usepackage{mathrsfs}
\usepackage{mathtools}

\begin{document}
Intro
\newline
\begin{subequations}
\label{DualCorrespondenceKetBra}
\begin{minipage}[t]{0.25\textwidth}
    \begin{equation}
    \label{DualCorrespHilbSpaces}
        \tilde{\mathscr{H}} \stackon{ $ \iff $ }{ \emph{DC} } \mathscr{H},
    \end{equation}
\end{minipage}\hfill
\begin{minipage}[t]{0.25\textwidth}
    \begin{equation}
    \label{BraKetCorrPsi}
        \bra{\psi} \stackon{ $ \iff $ }{ \emph{DC} } \ket{\psi},
    \end{equation}
\end{minipage}\hfill
\begin{minipage}[t]{0.25\textwidth}
    \begin{equation}
    \label{EigenBraKetCorr}
        \text{and } \bra{a'},\bra{a''},... \stackon{ $ \iff $ }{\emph{DC}} \ket{a'}, \ket{a''},... \quad ,
    \end{equation}
\end{minipage}
\end{subequations}
\newline
\newline
\newline
Outro
\end{document}

I am new to latex and have used this environment for side to side subequations in my text on a number of occasions now. Usually, by tweaking the \textwidth setting, I was able to make it look ok, but now the equations are either not displayed in the same line (too small value of textwidth, it seems to me) or the line goes way beyond the page layout (too large value of textwidth). If not so much space was left in between the subequations, I think it should fit into a single line just fine. Basically the question is, how do I make this look good? :)

Answer 1

The reason this looks ugly is because you are trying to fit more into one line than can comfortably fit. Adding the following two lines to the pramble

\usepackage{physics}
\usepackage[scr,scaled=1.1]{rsfso}

and some enclosing this within a \begin{document} and \end{document}, this seems to compile to (putting some \fbox commands around the minipages to show how big these are):

Basically the question is, how do I make this look good?

I would abandon trying to fit this all into one line as it will all just be too cramped, and so I would write:

\documentclass[a4paper, 12pt,twoside=on, listof=totoc, bibliography=totoc]{scrreprt}
\usepackage{amsmath}
\usepackage{stackengine}
\usepackage{physics}
\usepackage{mathtools}
\usepackage[scr,scaled=1.1]{rsfso} 
\begin{document}
\begin{subequations}
\begin{gather}
\label{DualCorrespHilbSpaces}
\tilde{\mathscr{H}} \stackon{ $ \iff $ }{ \emph{DC} } \mathscr{H},
\\
\label{BraKetCorrPsi}
\bra{\psi} \stackon{ $ \iff $ }{ \emph{DC} } \ket{\psi},
\\
\shortintertext{and}
\label{EigenBraKetCorr}
\bra{a'},\bra{a''},... \stackon{ $ \iff $ }{\emph{DC}} \ket{a'}, \ket{a''},...
\end{gather}
\end{subequations}
\end{document}

which gives

Answer 2

You can make all three subequations fit on a line if you (a) replace all three instances of \stackon{ $ \iff $ }{ \emph{DC} } with \overset{DC}{\iff}, (b) drop the extra commas and the "and" conjunction, and (c) increase the width of the third minipage from 0.25\textwidth to 0.47\textwidth.

\documentclass[a4paper, 12pt]{scrreprt}
\usepackage{braket,mathrsfs,mathtools}
\usepackage[margin=2.5cm]{geometry} % set page size parameters suitably

\begin{document}
\setcounter{chapter}{3} % just for this example

\begin{subequations}\label{DualCorrespondenceKetBra}
\begin{minipage}[t]{0.25\textwidth}
    \begin{equation}\label{DualCorrespHilbSpaces}
    \tilde{\mathscr{H}} \overset{DC}{\iff} \mathscr{H}
    \end{equation}
\end{minipage}\hfill%
\begin{minipage}[t]{0.25\textwidth}
    \begin{equation}\label{BraKetCorrPsi}
    \bra{\psi} \overset{DC}{\iff} \ket{\psi}
    \end{equation}
\end{minipage}\hfill%
\begin{minipage}[t]{0.47\textwidth}
    \begin{equation}\label{EigenBraKetCorr}
    \bra{a'},\bra{a''},\dotsc \overset{DC}{\iff} 
        \ket{a'}, \ket{a''},\dotsc 
    \end{equation}
\end{minipage}
\end{subequations}
\end{document}

Answer 3

If you are determined to have these all on the same line then you can adapt this solutionto Labelled in-line equation to give something like:

\documentclass[a4paper, 12pt,twoside=on, listof=totoc, bibliography=totoc]{scrreprt}
\usepackage{amsmath}
\usepackage{stackengine}
\usepackage{physics}
\usepackage{mathtools}
\usepackage[scr,scaled=1.1]{rsfso} 


\makeatletter
\newcommand*{\inlineequation}[2][]{%
\begingroup
% Put \refstepcounter at the beginning, because
% package `hyperref' sets the anchor here.
\refstepcounter{equation}%
\ifx\\#1\\%
\else
\label{#1}%
\fi
% prevent line breaks inside equation
\relpenalty=10000 %
\binoppenalty=10000 %
\ensuremath{%
% \displaystyle % larger fractions, ...
#2%
}%
~\@eqnnum
\endgroup
}
\makeatother

\begin{document}
\inlineequation[DualCorrespHilbSpaces]{
\tilde{\mathscr{H}} \stackon{ $ \iff $ }{ \emph{DC} } \mathscr{H}}, \hfill
\inlineequation[BraKetCorrPsi]{
\bra{\psi} \stackon{ $ \iff $ }{ \emph{DC} } \ket{\psi}}, and \hfill 
\inlineequation[EigenBraKetCorr]{
\bra{a'},\bra{a''},... \stackon{ $ \iff $ }{\emph{DC}} \ket{a'}, \ket{a''},...}

\eqref{DualCorrespHilbSpaces}, \eqref{BraKetCorrPsi}, and \eqref{EigenBraKetCorr} are interesting.
\end{document}

where you can then add \hfill as much or as little as you want without specifying the width, which is okay for these types of inline equations.