can you help me please to program with FreeFem++ the Following non linear problem: $$ \dfrac{\partial u}{\partial t} - \Delta u + F(u)= f(x,t), \ x \in (0,1)^2, t \in [0,T] $$ where $F$ in non linear function, for example $F(u)= 2u-\sin(u)$ and $f(x,t)= \sin(2\pi x)\sin(2\pi y)t^2e^{-t}$ with initial condition $u(x,0)=0$ and periodic boundary conditions.
I try to use fixed point, but i'm lost. Thank you in advance to help me.
Best regards