Exponential Time Differencing Runge-Kutta Method for Allen-Cahn Dynamics

1. Exponential time difference method with 1st order Runge-Kutta Method [m file];
2. Exponential time difference method with 2nd order Runge-Kutta Method [m file];
3. Exponential time difference method with 4th order Runge-Kutta Method [m file];