\documentclass[]{jsbook}
\usepackage{psfrag,graphicx,color,defvar2,eclepsf,othermac}
\pagestyle{empty}
\begin{document}
\begin{eqnarray*}
 U(k) &=& \frac{N(\theta(k)) - P(\theta(k))}{N(\theta(k)) + P(\theta(k))}
  \, G(D(k)) \, U_{max}
\label{eq-fi:stabilizing}
\\
\\
 &=& [2N(\theta(k))-1] \, G(D(k)) \, U_{max}
\end{eqnarray*}
\end{document}
