\begin{equation}
    \mathbf{M_2}=\mathbf{M_1}*\mathbf{W}_{RKF} =  \sum_{n=0}^{N-1}\left(\mathbf{M_1} * [L_r^{\theta_n}\mathbf{W}]\right), \theta_n = \frac{2\pi}{N}n.
    \label{eq:rkf}
\end{equation}
