说明：  用fortran编写的解常微分方程的代码，包括：euler方法、改进的euler方法、RK4方法，二阶常微分方程rk4方法。-some code for newer practice
(Differential coding shoes, comprising: euler method, the improved euler method, RK4 method, rk4 second-order ordinary differential equation.-some code for newer practice)