使用龙格库塔法求解微分方程，建立火箭模型，大气密度用函数计算，对比两种改进型的高度，速度及距离随时间的变化规律。-Using the Runge-Kutta method to solve differential equations, build model rockets, air density is calculated using the function, comparison of the two modified height, speed and distance variat