x1是第一类数据，x2 是第二类数据，每一列代表一个样本（两个特征）。绿色虚线是线性分类器产生的边界；蓝色实线是二次线性分类器产生的边界。-x1 is the first type data , x2 is the second type of data, and each column represents a sample (two features). Green dotted line is the boundary linear classifier generated　solid blue line is the border secondary linear classifier generated.