欧拉算法，基本思想是迭代。其中分为前进的EULER法、后退的EULER法、改进的EULER法。所谓迭代，就是逐次替代，最后求出所要求的解，并达到一定的精度。误差可以很容易的计算出来。-Euler algorithm, the basic idea is iterative. THE EULER method which is divided into forward and backward EULER ' method, improved EULER method. Called ite