说明：  Runge-Kutta法中最常用的是：四阶五级变步长算法。德国学者Felhberg对传统Runge-Kutta法进行了改进，得到了四阶五级变步长算法，也叫FRK算法。下面是标准四阶龙格-库塔法的Matlab程序
(Runge-Kutta method most commonly used are: FOURTH ORDER five variable step algorithm. German scholars Felhberg traditional Runge-Kutta method is improved to give a fourth-order five variable step algorithm, also called FRK algorithms. Here is the standard Runge- Kutta method of Matlab program)