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\begin{align}
 \Delta M_\mathrm{r}^\mathrm{k} & = -k_\mathrm{r} \Delta \theta_\mathrm{r} \\
 M_\mathrm{r,t+\Delta t}^\mathrm{k} & = M_\mathrm{r,t}^\mathrm{k} + \Delta M_\mathrm{r}^\mathrm{k} \\
 |M_\mathrm{r,t+\Delta t}^\mathrm{k}| & \leq M_\mathrm{r}^\mathrm{m} \\
 M_\mathrm{r}^\mathrm{m} & = \mu_\mathrm{r} R^* F_\mathrm{n}
\end{align}

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