说明：  所编子程序为标准四阶龙格库塔解常微分方程的程序，可以不作修改直接使用。再则，主程序当中用一个方程验证其正确性，并可以输出函数的一阶导。
(Subroutine, compiled by a standard fourth order Runge-Kutta ordinary differential equation solution procedure can be used directly without modification. Furthermore, the main program with an equation which verify its accuracy, and can output function of a derivative.)