说明：  应用bp算法实现对iris数据库的分类，iris数据库是人们广泛使用的用于模式分类的实例系统。它含有150个例子，分为三类，每个类由四个实数特征值描述，分别表示萼片（sepal ）长度，萼片宽度，花瓣（petal ）长度，花瓣宽度。问题是根据这四个特性值分类三种iris 植物，输入为四个特征值和类别 （5.1 3.5 1.4 0.2 0），输出算法分类结果
(Bp algorithms applied to the iris database, the classification, iris database is widely used for pattern classification of the instances of the system. It contains 150 examples, divided into three categories, each class consists of four real eigenvalue description, respectively sepals (sepal) length, sepal width, petal (petal) length, petal width. The problem is classified according to the value of these four characteristics of three kinds of iris plants, enter the four characteristic values and categories (5.1 3.5 1.4 0.2 0), the output algorithm classification results)