请大家帮帮忙看看下面这个非线性的式子，写成Fokker-Planck equation use Ito interpolation 要怎么写阿？The relative return $x_{(t+1)}$ at time  ${t+1}$ is defined as:
\begin{equation}   
x _{(t+1)}=ax _{(t)}-bx _{(t)}^3+\sqrt{c{x_{(t)}^2+k}}\varepsilon_{(t)}
\end{equation}
Here the variable $a$,  $b$ and $c$ are parameters and $\varepsilon_{(t)}$ is a white noise process.


万分感谢！