4阶变步长龙格-库塔法解dy=fun(x,y)型方程,根据算法编写。

4阶变步长龙格-库塔法解dy=fun(x,y)型方程,根据算法编写。-4th order variable step Changlong Grid- Kutta method solution of dy = fun (x, y)-type equation, according to the preparation algorithm.