ode4

代码说明：

  经常看到很多朋友问定步长的龙格库塔法设置问题，下面吧定步长四阶龙格库塔程序贴出来，有需要的可以看看 (Often see many of my friends ask determining step Runge-Kutta method set problem, the following step you set the fourth-order Runge-Kutta procedures paste out, there is a need to look at the)