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\begin{document}
\begin{equation*}
  \underbrace{\begin{bmatrix} J_h \\ K_h \end{bmatrix}}_{\bar J_h} \dot\theta =
  \underbrace{\begin{bmatrix} G^T & 0 \\ 0 & I \end{bmatrix}}_{\bar G^T} 
  \begin{bmatrix} \dot x \\ v_N \end{bmatrix},
\end{equation*}
\end{document}