I am using twocolumn svjour3 template to submit a paper. I want to write long equations as a single column. But I get an error message

Question

Here's what I did: I have the same problem with long equations in the svjour3 document class. I want to display the long equations as a single column. I tried

\documentclass[twocolumn]{svjour3}          % twocolumn
\usepackage{widetext}
\begin{document}

\begin{widetext}
\begin{eqnarray}
%long equation here
\end{eqnarray}
\end{widetext}


\end{document}

but I get the error message:

! LaTeX Error: Environment widetext undefined.

Please help. Thanks!