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\begin{equation*}
\begin{aligned}
  A &=\left.\frac{\partial f(x, u)}{\partial x}\right|_{x_e, u_e} &\quad
  B &= \left.\frac{\partial f(x, u)}{\partial u}\right|_{x_e, u_e} \\
  C &= \left.\frac{\partial h(x, u)}{\partial x}\right|_{x_e, u_e} &\quad
  D &= \left.\frac{\partial y(x, u)}{\partial u}\right|_{x_e, u_e}
\end{aligned}
\end{equation*}
\end{document}