# Switch from double to single column in the same page, for insert long equation

When I using overleaf template here, I changed the codes to \documentclass[twocolumn]{svjour3}

I have long equations, so I want to the equation cross the two column. I try change to \onecolumn, and then using multicol package, but I can't work it out.

Simple codes as following:

\documentclass[twocolumn]{svjour3}       % onecolumn (second format)
\usepackage{lipsum}
\begin{document}

}
\subtitle{Do you have a subtitle?\\ If so, write it here}

\author{First Author         \and
Second Author %etc.
}

\institute{F. Author \at
Tel.: +123-45-678910\\
Fax: +123-45-678910\\
\email{fauthor@example.com}           %  \\
%             \emph{Present address:} of F. Author  %  if needed
\and
S. Author \at
}

% The correct dates will be entered by the editor

\maketitle

\lipsum[1-3]
$$\label{key} AcceptAcceptAccept AcceptAcceptAcceptAcceptAcceptAcceptAcceptAccept$$
\lipsum[1]

\end{document}

You can use the strip environment from the cuted package (sttools bundle):

\documentclass[twocolumn]{svjour3} % onecolumn (second format)
\usepackage{cuted}
\setlength{\stripsep}{0pt}
\usepackage{lipsum}
\begin{document}

}
\subtitle{Do you have a subtitle?\\ If so, write it here}

\author{First Author \and
Second Author %etc.
}

\institute{F. Author \at
Tel.: +123-45-678910\\
Fax: +123-45-678910\\
\email{fauthor@example.com} % \\
% \emph{Present address:} of F. Author % if needed
\and
S. Author \at
}

$$\label{key} AcceptAcceptAccept AcceptAcceptAcceptAcceptAcceptAcceptAcceptAccept$$