\documentclass[]{jsbook}
\usepackage{psfrag,graphicx,color,defvar2,eclepsf,othermac}
\pagestyle{empty}
\begin{document}
{
% \newcommand{\dd}{{\rm d}}
\begin{eqnarray*}
 \frac{\dd x}{\dd t} &=& -y -z
\\
 \frac{\dd y}{\dd t} &=&  x + a y
\\
 \frac{\dd z}{\dd t} &=& b + z(x-c)
\end{eqnarray*}
}
\end{document}
