[Tex/LaTex] Matrix exceeds column width for IEEEtran format

Question

I'm trying to fit this matrix within one column. But it is exceeding the limit and overlapping with the column beside of it.

\documentclass{IEEEtran}
\usepackage{amsmath}

\begin{document}
$e^{At}$ = \[ \left[ \begin{array}{ccc}
3*e^{-t}-3*e^{-2t}+e^{-3t} & \dfrac{5}{2}*e^{-t}-4*e^{-2t}+\dfrac{3}{2}*e^{-3t} & \dfrac{1}{2}*e^{-t}-e^{-2t}+\dfrac{1}{2}*e^{-3t} \\\\
-3*e^{-t}+6*e^{-2t}-3*e^{-3t} & \dfrac{-5}{2}*e^{-t}+8*e^{-2t}-\dfrac{9}{2}*e^{-3t} & \dfrac{-1}{2}*e^{-t}+2*e^{-2t}-\dfrac{3}{2}*e^{-3t} \\\\
3*e^{-t}-12*e^{-2t}+9*e^{-3t} & \dfrac{5}{2}*e^{-t}-16*e^{-2t}+\dfrac{27}{2}*e^{-3t} & \dfrac{1}{2}*e^{-t}-4*e^{-2t}+\dfrac{9}{2})*e^{-3t} \end{array} \right]\]
\end{document}

Answer 1

I suggest you use the cuted package, and its strip environment, so as the equation spreads over two columns. I also reduced the size of the fraction coefficients using the \mfrac command (medium sized fractions), from the nccmath package:

\documentclass{ieeeconf}
\usepackage[utf8]{inputenc}
\usepackage{lipsum}
\usepackage{mathtools, nccmath}
\usepackage{cuted}
\input{insbox.tex}

\begin{document}
\lipsum[1]
\setlength\stripsep{\partopsep}%

\begin{strip}
  \[
    e^{At}=
    \begin{bmatrix}
      3 e^{-t}-3 e^{-2t}+e^{-3t} & \mfrac{5}{2} e^{-t}-4 e^{-2t}+\mfrac{3}{2} e^{-3t} & \mfrac{1}{2} e^{-t}-e^{-2t}+\mfrac{1}{2} e^{-3t} \\[2ex]
      -3 e^{-t}+6 e^{-2t}-3 e^{-3t} & -\mfrac{5}{2} e^{-t}+8 e^{-2t}-\mfrac{9}{2} e^{-3t} & -\mfrac{1}{2} e^{-t}+2 e^{-2t}-\mfrac{3}{2} e^{-3t} \\[2ex]
      3 e^{-t}-12 e^{-2t}+9 e^{-3t} & \mfrac{5}{2} e^{-t}-16 e^{-2t}+\mfrac{27}{2} e^{-3t} & \mfrac{1}{2} e^{-t}-4 e^{-2t}+\mfrac{9}{2} e^{-3t}
    \end{bmatrix}
  \]
\end{strip}
\lipsum[3-6]

\end{document}