\documentclass[12pt]{article}
\usepackage{amssymb,amsmath,amscd,concmath,amsfonts}
\usepackage{color}
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\begin{document}
\begin{equation*}
  \aligned 
    H[k+1] &= H[k] + b_r(u) H[k] - a L[k] H[k], \\
    L[k+1] &= L[k] + c L[k] H[k] - d_f L[k],
  \endaligned
\end{equation*}
\end{document}