I want to set the width of picture as two columns of my article of three columns

Question

I'm writing an article with three columns, and I use the code 

\usepackage{multicol}
\begin{multicols}{3}
\end{multicols}

Now I want to insert a picture which occupies two columns size. How could I accomplish it?

Answer 1

multicol doesn't support floats but you can always position an image by hand, leaving space in the spanned columns;

\documentclass{article}
\usepackage{capt-of}
\usepackage{multicol}

\def\a{\stepcounter{enumi}\Roman{enumi}: \roman{enumi} one two three (\theenumi) four five. }
\def\b{\a\a Green yellow black white. \a\a\a}
\def\c{\b\b\par Apple pear orange. \b\par}

\begin{document}

\begin{multicols}{3}
\c\b\b

\rlap{\begin{minipage}{\dimexpr2\columnwidth+\columnsep}
\centering
\begin{picture}(100,100)
\put(50,95){\line(1,-3){25}}
\put(50,95){\line(-1,-3){25}}
\put(25,20){\line(1,0){50}}
\put(45,20){\line(0,-1){15}}
\put(55,20){\line(0,-1){15}}
\thicklines
\put(20,5){\line(1,0){60}}
\end{picture}
\captionof{figure}{A Christmas Tree}
\end{minipage}}

\c
\columnbreak
\vspace*{11\baselineskip}\c\c
\end{multicols}
\end{document}