دستور \hline خط افقی را برای شما رسم میکند.
\begin{equation}
\Xi = \begin{pmatrix}
\xi_1^{\mathrm{in} \, \phi} & \xi_2^{\mathrm{in} \, \phi} & \xi_3^{\mathrm{in} \, \phi}\\
\hline
\left\langle \phi_1 | \xi_1 \right\rangle & \left\langle \phi_1 | \xi_2 \right\rangle & \left\langle \phi_1 | \xi_3 \right\rangle \\
\left\langle \phi_2 | \xi_1 \right\rangle & \left\langle \phi_2 | \xi_2 \right\rangle & \left\langle \phi_2 | \xi_3 \right\rangle \\
\left\langle \phi_3 | \xi_1 \right\rangle & \left\langle \phi_3 | \xi_2 \right\rangle & \left\langle \phi_3 | \xi_3 \right\rangle
\end{pmatrix}
\end{equation}
