0

When I split a long equation using split or aligned in a document with two columns (through loading aistats2021 package), the splitted part goes towards second column instead of staying inside first column. Moreover, I am getting overfull \hbox warning.

\documentclass[twoside]{article}

\usepackage{aistats2021}
\begin{document}
We recall the optimization problem here which is given below. Now consider why this broken this way.
\begin{equation}\label{Eq:pi-mirror-descent}
\begin{split}
\argmax_{\pi_h \in \Delta(\cA \mid \cS)} \mathbb{E}_{\pi^{k-1}} \Bigl [ \langle Q_h^{k-1}(s_h, \cdot),\pi_h(\cdot \given s_h)\rangle_\cA +\\
&\frac{1}{\alpha}\mathcal{D}_{KL}\bigl(\pi_h(\cdot \mid s_h) \|\ \pi_h^{k-1}(\cdot \mid s_h)\bigr) \bigm]
\end{split}
\end{equation}
\end{document}

enter image description here

And here is the aistats2021.sty file for reproducing the error.

% File:  aistats2021.sty

% Modified by Robert Giaquinto and Krikamol Muandet 2021: changed
% venue, year, and volume number. Adjust spacing in the copyright box.
%
% Modified by Marcello Restelli, 2020: changed \evensidemargin and
% \oddsidemargin in order to center the text with respect to the page.
% Removed author names and affiliation when the paper is submitted.
% Added command to display acknowledgments only in the final version.
%
% Modified by Roberto Calandra, 2019: introduced parametric structure to
% change venue, year, and volume number. This will make life easier
% for future organizers :)
%
% Modified Atsushi Miyauchi, Mirai Tanaka and Akiko Takeda, 2018: changed venue,
% year, volume number, and heading for the references, and removed tiny bugs.
%
% Modified Fernando Perez-Cruz, 2017: changed venue, year, and volume number.
%
% Modified Scott Alfeld, 2016: changed venue, year, and volume number.
%
% Modified Zoltan Szabo, 2015: change venue, year, volume number.
%
% Modified Antti Honkela, 2013: change venue, year
%
% Modified Miro Dudik, 2011, 2012: change venue, year and volume number
%
% Modified Geoff Gordon, 2010: change to 2011
%
% Modified Mauricio Alvarez, 2009. Headings for the manuscript when
% being under review and additional changes so that the headings are
% automatically obtained from the title and author fields from the tex
% file. Also changes to the year 2009 for 2010 where it appeared.
%
% Modified Mauricio Alvarez, 2009. Copyright Notice and commands for headings
%
%
% Originally this file contains the LaTeX formatting parameters for the Morgan
% Kaufmann two column, 8 1/2 by 11 inch proceedings format.

\NeedsTeXFormat{LaTeX2e}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Content to be changed from year to year

\ProvidesPackage{aistats2021}[2020/08/23 AISTATS2021 submission/camera-ready style file]

\newcommand{\@conferenceordinal}{24\textsuperscript{th}}
\newcommand{\@conferenceyear}{2021}
\newcommand{\@conferencelocation}{San Diego, California, USA}
\newcommand{\@conferencevolume}{130}  % To be assigned by JMLR

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\RequirePackage{amsmath}

% Create acknowledgments -- only if the option 'final' is activated
\providecommand{\acknowledgments}[1]{}
\newcommand{\ackaccepted}[1]{%
\subsubsection*{Acknowledgments} #1
}

\DeclareOption{accepted}{\renewcommand{\statePaper}{\acceptedPaper}%
                         \renewcommand{\Notice@String}{\AISTATS@appearing}%
                         \renewcommand{\acknowledgments}{\ackaccepted}}

\newcommand{\statePaper}{0}
\newcommand{\acceptedPaper}{1}
\newcommand{\Notice@String}{Preliminary work. Under review by AISTATS \@conferenceyear. Do not distribute.}
\newcommand{\AISTATS@appearing}{Proceedings of the \@conferenceordinal\,International Conference on Artificial
  Intelligence and Statistics (AISTATS) \@conferenceyear,  \@conferencelocation\@. PMLR: Volume  \@conferencevolume. Copyright
  \@conferenceyear\/ by the author(s).}

\ProcessOptions\relax

\evensidemargin -0.125in
\oddsidemargin -0.125in
\setlength\topmargin{-25pt} \setlength\textheight{9.25in}
\setlength\textwidth{6.75in} \setlength\columnsep{0.25in}
\newlength\titlebox \setlength\titlebox{2.375in}
\setlength\headheight{10pt} \setlength\headsep{15pt}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%% To include the copyright legend at the end of
%%%% the first column of the first page. Adapted from ICML09.sty
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\def\ftype@copyrightbox{8}
\def\@copyrightspace{
% Create a float object positioned at the bottom of the column.  Note
% that because of the mystical nature of floats, this has to be called
% before the first column is populated with text (e.g., from the title
% or abstract blocks).  Otherwise, the text will force the float to
% the next column.  -- TDRL.
\@float{copyrightbox}[b]
\begin{center}
\setlength{\unitlength}{1pc}
\begin{picture}(20,2.5)
% Create a line separating the main text from the note block.
% 4.818pc==0.8in.
\put(0,3.5){\line(1,0){4.818}}
% Insert the text string itself.  Note that the string has to be
% enclosed in a parbox -- the \put call needs a box object to
% position.  Without the parbox, the text gets splattered across the
% bottom of the page semi-randomly.  The 19.75pc distance seems to be
% the width of the column, though I can't find an appropriate distance
% variable to substitute here.  -- TDRL.
\put(0,0){\parbox[b]{19.75pc}{\small \Notice@String}}
\end{picture}
\end{center}
\end@float}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\setlength\footskip{0pt}
\thispagestyle{empty}     \pagestyle{empty}
\flushbottom \twocolumn \sloppy

\def\addcontentsline#1#2#3{}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%     Definition of maketitle (includes title and author)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\RequirePackage{fancyhdr}

% box to check the size of the running head
\newbox\titrun
\newbox\autrun

% general page style
\pagestyle{fancy}
\renewcommand{\headrulewidth}{0pt}

\fancyhead{}
\fancyfoot{}

% definition to set running head title and running head author
\def\runningtitle#1{\gdef\@runningtitle{#1}}
\def\runningauthor#1{\gdef\@runningauthor{#1}}

\long\def\aistatstitle#1{

   %\renewcommand{\headrulewidth}{0.5pt}

   \gdef\@runningheadingerrortitle{0}

   % If paper is under review print this as headings

   \ifnum\statePaper=0
    {
     \gdef\@runningtitle{Manuscript under review by AISTATS \@conferenceyear}
    }
   \fi

   % If the paper is accepted, print the title or the running title as heading.

   \ifnum\statePaper=1
   {
   \ifx\undefined\@runningtitle
    {
    \gdef\@runningtitle{#1}
    }
   \fi
   }
   \fi

   \ifnum\@runningheadingerrortitle=0
         {
         \global\setbox\titrun=\vbox{\small\bfseries\@runningtitle}%
         \ifdim\wd\titrun>\textwidth%
            {\gdef\@runningheadingerrortitle{2}
             \gdef\@messagetitle{Running heading title too long}
            }%
         \else\ifdim\ht\titrun>10pt
              {\gdef\@runningheadingerrortitle{3}
              \gdef\@messagetitle{Running heading title breaks the line}
              }%
              \fi
          \fi
         }
    \fi

   \ifnum\@runningheadingerrortitle>0
     {
        \fancyhead[CE]{\small\bfseries\@messagetitle}
        \ifnum\@runningheadingerrortitle>1
           \typeout{}%
           \typeout{}%
           \typeout{*******************************************************}%
           \typeout{Running heading title exceeds size limitations for running head.}%
           \typeout{Please supply a shorter form for the running head}
           \typeout{with \string\runningtitle{...}\space just after \string\begin{document}}%
           \typeout{*******************************************************}%
           \typeout{}%
           \typeout{}%
        \fi
     }
  \else
     {
          \fancyhead[CE]{\small\bfseries\@runningtitle}
     }
  \fi

  \hsize\textwidth
  \linewidth\hsize \toptitlebar {\centering
  {\Large\bfseries #1 \par}}
 \bottomtitlebar \vskip 0.2in plus 1fil minus 0.1in
}

\long\def\aistatsauthor#1{

   \gdef\@runningheadingerrorauthor{0}

   % If the paper is under review, print this message as heading.

   \ifnum\statePaper=0
    {
     \gdef\@runningauthor{Manuscript under review by AISTATS \@conferenceyear}
    }
   \fi

   % If the paper is accepted, print the author names or runningauthor as heading.

   \ifnum\statePaper=1
   {
   \ifx\undefined\@runningauthor%
    {
   \gdef\@runningauthor{\def\and{\unskip{,}\enspace}\def\And{\unskip{,}\enspace}\def\AND{\unskip{,}\enspace}
   #1}
    }
   \fi
    }
   \fi

  \ifnum\@runningheadingerrorauthor=0
      {
      \global\setbox\autrun=\vbox{\small\bfseries\@runningauthor}
      \ifdim\wd\autrun>\textwidth%
            {\gdef\@runningheadingerrorauthor{2}
             \gdef\@messageauthor{Running heading author too long}
            }%
         \else\ifdim\ht\autrun>10pt
              {\gdef\@runningheadingerrorauthor{3}
              \gdef\@messageauthor{Running heading author breaks the line}
              }%
              \fi
          \fi
      }
  \fi

  \ifnum\@runningheadingerrorauthor>0
     {
       \fancyhead[CO]{\small\bfseries\@messageauthor}
       \ifnum\@runningheadingerrorauthor>1
           \typeout{}%
           \typeout{}%
           \typeout{*******************************************************}%
           \typeout{Running heading author exceeds size limitations for running head.}%
           \typeout{Please supply a shorter form for the running head}
           \typeout{with \string\runningauthor{...}\space just after \string\begin{document}}%
           \typeout{*******************************************************}%
           \typeout{}%
           \typeout{}%
      \fi
     }
  \else
     {
     \fancyhead[CO]{\small\bfseries\@runningauthor}
     }
  \fi


    \ifnum\statePaper=0
    {
        {\def\and{\unskip\enspace{\rm and}\enspace}%
        \def\And{\end{tabular}\hss \egroup \hskip 1in plus 2fil
                \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}%
        \def\AND{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}
        \def\ANDD{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}
            \hbox to \linewidth\bgroup \hfil\hfil
            \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries Anonymous Author
                                \end{tabular}
            \hss\egroup
            \hfil\hfil\egroup}
    }
    \else
    {
        {\def\and{\unskip\enspace{\rm and}\enspace}%
        \def\And{\end{tabular}\hss \egroup \hskip 1in plus 2fil
                \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}%
        \def\AND{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}
        \def\ANDD{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries}
            \hbox to \linewidth\bgroup \hfil\hfil
            \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}\bfseries #1
                                \end{tabular}
            \hss\egroup
            \hfil\hfil\egroup}
    }
   \fi
}



\long\def\aistatsaddress#1{
     \ifnum\statePaper=0
    {
        {\def\and{\unskip\enspace{\rm and}\enspace}%
        \def\And{\end{tabular}\hss \egroup \hskip 1in plus 2fil
                \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c} }%
        \def\AND{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt  \bgroup \hss \begin{tabular}[t]{c}}
        \def\ANDD{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth \bgroup \hfil\hfil
                    \hbox to 0pt  \bgroup \hss\begin{tabular}[t]{c}\bfseries}
            \hbox to \linewidth\bgroup \hfil\hfil
            \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c}
            Anonymous Institution
            \end{tabular}
            \hss\egroup
            \hfil\hfil\egroup}
        \vskip 0.3in plus 2fil minus 0.1in
    }
    \else
    {
        {\def\and{\unskip\enspace{\rm and}\enspace}%
        \def\And{\end{tabular}\hss \egroup \hskip 1in plus 2fil
                \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c} }%
        \def\AND{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth\bgroup \hfil\hfil
                    \hbox to 0pt  \bgroup \hss \begin{tabular}[t]{c}}
        \def\ANDD{\end{tabular}\hss\egroup \hfil\hfil\egroup
                \vskip 0.25in plus 1fil minus 0.125in
                \hbox to \linewidth \bgroup \hfil\hfil
                    \hbox to 0pt  \bgroup \hss\begin{tabular}[t]{c}\bfseries}
            \hbox to \linewidth\bgroup \hfil\hfil
            \hbox to 0pt\bgroup\hss \begin{tabular}[t]{c} #1
                                \end{tabular}
        \hss\egroup
        \hfil\hfil\egroup}
    \vskip 0.3in plus 2fil minus 0.1in
    }
   \fi
}

\renewcommand{\headrulewidth}{0.5pt}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%  Definition of abstract environment
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\renewenvironment{abstract}
{\@copyrightspace\centerline{\large\bfseries
Abstract}\vspace{0.5ex}\begin{quote}}{\par\end{quote}\vskip 1ex}

% sections with less space
\def\section{\@startsection {section}{1}{\z@}{-2.0ex plus
    -0.5ex minus -.2ex}{1.5ex plus 0.3ex minus .2ex}{\large\bfseries\raggedright}}
\def\subsection{\@startsection{subsection}{2}{\z@}{-1.8ex plus
    -0.5ex minus -.2ex}{0.8ex plus .2ex}{\normalsize\bfseries\raggedright}}
\def\subsubsection{\@startsection{subsubsection}{3}{\z@}{-1.5ex plus
   -0.5ex minus -.2ex}{0.5ex plus .2ex}{\normalsize\bfseries\raggedright}}
\def\paragraph{\@startsection{paragraph}{4}{\z@}{1.5ex plus
   0.5ex minus .2ex}{-1em}{\normalsize\bfseries}}
\def\subparagraph{\@startsection{subparagraph}{5}{\z@}{1.5ex plus
   0.5ex minus .2ex}{-1em}{\normalsize\bfseries}}
\def\subsubsubsection{\vskip 5pt{\noindent\normalsize\rm\raggedright}}




% Footnotes
\footnotesep 6.65pt %
\skip\footins 9pt plus 4pt minus 2pt
\def\footnoterule{\kern-3pt \hrule width 5pc \kern 2.6pt }
\setcounter{footnote}{0}

% Lists and paragraphs
\parindent 0pt
\topsep 4pt plus 1pt minus 2pt
\partopsep 1pt plus 0.5pt minus 0.5pt
\itemsep 2pt plus 1pt minus 0.5pt
\parsep 2pt plus 1pt minus 0.5pt
\parskip .5pc


\leftmargin 2em \leftmargini\leftmargin \leftmarginii 2em
\leftmarginiii 1.5em \leftmarginiv 1.0em \leftmarginv .5em
\leftmarginvi .5em
\labelwidth\leftmargini\advance\labelwidth-\labelsep \labelsep 5pt

\def\@listi{\leftmargin\leftmargini}
\def\@listii{\leftmargin\leftmarginii
   \labelwidth\leftmarginii\advance\labelwidth-\labelsep
   \topsep 2pt plus 1pt minus 0.5pt
   \parsep 1pt plus 0.5pt minus 0.5pt
   \itemsep \parsep}
\def\@listiii{\leftmargin\leftmarginiii
    \labelwidth\leftmarginiii\advance\labelwidth-\labelsep
    \topsep 1pt plus 0.5pt minus 0.5pt
    \parsep \z@ \partopsep 0.5pt plus 0pt minus 0.5pt
    \itemsep \topsep}
\def\@listiv{\leftmargin\leftmarginiv
     \labelwidth\leftmarginiv\advance\labelwidth-\labelsep}
\def\@listv{\leftmargin\leftmarginv
     \labelwidth\leftmarginv\advance\labelwidth-\labelsep}
\def\@listvi{\leftmargin\leftmarginvi
     \labelwidth\leftmarginvi\advance\labelwidth-\labelsep}

\abovedisplayskip 7pt plus2pt minus5pt%
\belowdisplayskip \abovedisplayskip
\abovedisplayshortskip  0pt plus3pt%
\belowdisplayshortskip  4pt plus3pt minus3pt%

% Less leading in most fonts (due to the narrow columns)
% The choices were between 1-pt and 1.5-pt leading
\def\@normalsize{\@setsize\normalsize{11pt}\xpt\@xpt}
\def\small{\@setsize\small{10pt}\ixpt\@ixpt}
\def\footnotesize{\@setsize\footnotesize{10pt}\ixpt\@ixpt}
\def\scriptsize{\@setsize\scriptsize{8pt}\viipt\@viipt}
\def\tiny{\@setsize\tiny{7pt}\vipt\@vipt}
\def\large{\@setsize\large{14pt}\xiipt\@xiipt}
\def\Large{\@setsize\Large{16pt}\xivpt\@xivpt}
\def\LARGE{\@setsize\LARGE{20pt}\xviipt\@xviipt}
\def\huge{\@setsize\huge{23pt}\xxpt\@xxpt}
\def\Huge{\@setsize\Huge{28pt}\xxvpt\@xxvpt}

\def\toptitlebar{
\hrule height4pt
\vskip .25in}

\def\bottomtitlebar{
\vskip .25in
\hrule height1pt
\vskip .25in}

\renewenvironment{thebibliography}[1]
     {\subsubsection*{\refname}%
      \@mkboth{\MakeUppercase\refname}{\MakeUppercase\refname}%
      \list{\@biblabel{\@arabic\c@enumiv}}%
           {\settowidth\labelwidth{\@biblabel{#1}}%
            \leftmargin\labelwidth
            \advance\leftmargin\labelsep
            \@openbib@code
            \usecounter{enumiv}%
            \let\p@enumiv\@empty
            \renewcommand\theenumiv{\@arabic\c@enumiv}}%
      \sloppy
      \clubpenalty4000
      \@clubpenalty \clubpenalty
      \widowpenalty4000%
      \sfcode`\.\@m}
     {\def\@noitemerr
       {\@latex@warning{Empty `thebibliography' environment}}%
      \endlist}
      
      


2
  • 2
    you either ned to add an & to the first row or remove the & from the second row. Right now it is too long and is simply overlapping the right side. Oct 13, 2020 at 1:49
  • Where are defined \argmax and \given?
    – Zarko
    Oct 13, 2020 at 6:06

2 Answers 2

3
  • In your MWE are not defined \argmax nor \given nor \cA nor \cS, so it cannot be compiled, also is missed package amssymb for used \mathbb{...} command in equation.
  • use of the aistats2021 package is relevant to your problem only because it load amsmath package, so in MWE it can be replaced by option twocolumn in \documentclass and loading of amsmath package as is done in the MWE below
  • As solution of your problem you may consider to use ˙multlinemath environment defined in theamsmath` package. IN it I try to reproduce symbols in shoed in the image of your equation:
\documentclass[twocolumn,   % not needed when is loaded `aistats2021`
                twoside]{article}
%\usepackage{aistats2021}    % it is not relevant to your problem
\usepackage{amsmath,        % not needed when is loaded `aistats2021`
            amssymb}
\DeclareMathOperator*{\argmax}{arg\,max}
\DeclareMathOperator*{\given}{?}    % it is not known, in equation is replaced by `\mid`
% \cA   % it is not known, in equation is replaced by `\mathcal{A}`
% \cS   % it is not known, in equation is replaced by `\mathcal{S}`

\usepackage{lipsum}         % text filler     

\begin{document}
We recall the optimization problem here which is given below. Now consider why this broken this way.
\begin{multline}\label{Eq:pi-mirror-descent}
\argmax_{\pi_h \in \Delta(\mathcal{A} \mid \mathcal{S})} 
    \mathbb{E}_{\pi^{k-1}} \Bigl[ 
        \left\langle Q_h^{k-1}(s_h \mid \cdot),\pi_h(\cdot\mid s_h)\right\rangle_{\mathcal{A}} \\
 +\frac{1}{\alpha}\mathcal{D}_{KL}\bigl(\pi_h(\cdot \mid s_h) \|\ \pi_h^{k-1}(\cdot \mid s_h)\bigr) 
                            \Bigr]
\end{multline}
\lipsum % text filler 
\end{document}

enter image description here

Addendum: Considering comment of the @daleif, the preamble and equation on above MWE can be written as:

\documentclass[twocolumn, twoside]{article}
\usepackage{mathtools,       % needed, also when is loaded `aistats2021` which only provide `amsmath`
            amssymb}
\DeclareMathOperator*{\argmax}{arg\,max}
\DeclarePairedDelimiterX\given[2]()%        % <--- new
    {#1{}\delimsize\vert{}\mathopen{}#2}%   % <--- new
%\cA   % it is not known, in equation is replaced by `\mathcal{A}`
%\cS   % it is not known, in equation is replaced by `\mathcal{S}`

\usepackage{lipsum}         % text filler     

\begin{document}
We recall the optimization problem here which is given below. Now consider why this broken this way.
\begin{multline}\label{Eq:pi-mirror-descent}
\argmax_{\pi_h \in \Delta\given*{\mathcal{A}}{\mathcal{S}}} % <--- changed
    \mathbb{E}_{\pi^{k-1}} \Bigl[
        \left\langle Q_h^{k-1}  \given*{s_h}{\cdot},    % <--- changed
                     \pi_h      \given*{\cdot}{s_h}     % <--- changed
        \right\rangle_{\mathcal{A}} \\
% second line
 + \frac{1}{\alpha}\mathcal{D}_{KL}
    \left(\pi_h         \given*{s_h}{\cdot} % <--- changed
    \middle\|   % <--- new
          \pi_h^{k-1}   \given*{\cdot}{s_h} % <--- changed
    \right)
                            \Bigr]
    \end{multline}
\lipsum % text filler 
\end{document}

With these changes the equation now looks like:

enter image description here

6
  • Great, +1, better than mine...
    – MadyYuvi
    Oct 13, 2020 at 7:29
  • 1
    @MadyYuvi, well, I more focused on off-topic issues ... but many people more like your solution with use of the split (+1 for your suggestion). We will, what OP more liked (if (s)he will respond.
    – Zarko
    Oct 13, 2020 at 7:34
  • \given is likely to be | plus spacing. I never use \mid for this as it cannot be scaled. So I tend to use the \given defined in the \Set example in the mathtools manual
    – daleif
    Oct 13, 2020 at 9:04
  • @daleif, thanks for pointing me to given as defined in` mathtools`. I will have to read his documentation thoroughly again. I'm getting more and more forgetful ... See addendum in answer. Is better now?
    – Zarko
    Oct 13, 2020 at 12:15
  • Sort of, though here I don't see given as a function of two args, but rather pih as a function of one variable in which given can be used to mark the location of the |. I'm not 100% sure what the meaning of this equation is, especially the \|. But the s_h | \cdot seems to be something conditional (like in probability theory, A|B, as in A given B. Thus I'd write s_h \given \cdot to make it nicer to read both in code (and in output due to the extra spacing). I'd also use a macro to add the \cdot with a different spacing
    – daleif
    Oct 13, 2020 at 12:24
1

You have to give & sign where you want to align the breakings in split environment (as John Kormylo mentioned in his comment), also due to error I just removed \ from your code, please take care of that...

Generally while breaking operator sign + - X etc. should comes in the second line with a quad indentation, and the modified MWE is:

\documentclass[twoside]{article}

\usepackage{aistats2021}
\usepackage{amsfonts}

\begin{document}
We recall the optimization problem here which is given below. Now consider why this broken this way.
\begin{equation}\label{Eq:pi-mirror-descent}
\begin{split}
&argmax_{\pi_h \in \Delta(cA \mid cS)} \mathbb{E}_{\pi^{k-1}} \Bigl [ \langle Q_h^{k-1}(s_h, \cdot),\pi_h(\cdot given s_h)\rangle_cA \\
&\quad +\frac{1}{\alpha}\mathcal{D}_{KL}\bigl(\pi_h(\cdot \mid s_h) \|\ \pi_h^{k-1}(\cdot \mid s_h)\bigr) \bigm]
\end{split}
\end{equation}
\end{document}

Note: I've added amsfonts.sty to avoid the \mathbb error...

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