说明：  * 用改进的欧拉方法求解初值问题，其中一阶微分方程未y =f(x,y) * 初始条件为x=x[0]时,y＝y[0]. * 输入: f--函数f(x,y)的指针 * x--自变量离散值数组(其中x[0]为初始条件) * y--对应于自变量离散值的函数值数组(其中y[0]为初始条件) * h--计算步长 * n--步数 * 输出: x为说求解的自变量离散值数组 * y为所求解对应于自变量离散值的函数值数组
(* Improved Euler method to solve initial value problems, not an order differential equation y = f (x, y)* initial conditions for x = x [0], y = y [0].* Input : f-- function f (x, y)* x pointer-- from the array variable discrete values (x [0] for the initial conditions)* y-- corresponding to the variable discrete value of the function of the array (y [0] for the initial conditions)* h-- calculated step* n-- steps* output : Solving for x that the variable array* discrete values by solving y variables corresponding to the value of the discrete function arrays)