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%%  An UIT Edition example
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%%  Example 04-05-13 on page 43.
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%%  Copyright (C) 2010 Herbert Voss
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%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
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%%  See http://www.latex-project.org/lppl.txt for details.
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{15}
\renewcommand\theequation{4.\arabic{equation}}
\StartShownPreambleCommands
\setlength\arraycolsep{2pt}
\StopShownPreambleCommands
\begin{document}
\begin{eqnarray}
  B(r,\phi,\lambda) & = & \,\frac{\mu}{r}
    \Bigg[\sum_{n=2}^{\infty}\Bigg(\left(\frac{R_e}{r}\right)^n J_nP_n(s\phi)\nonumber\\
  & & {}+\sum_{m=1}^n \left( \frac{R_e}{r} \right) ^n
   (C_{nm}\cos m\lambda+S_{nm}\sin m\lambda)P_{nm}(s\phi) \Bigg)\Bigg]
\end{eqnarray}
\end{document}