n_classes = 3 n_estimators = 30 plot_colors = "ryb" cmap = plt.cm.RdYlBu plot_step = 0.02 # fine step width for decision surface contours plot_step_coarser = 0.5 # step widths for coarse classifier guesses RANDOM_SEED = 13 # fix the seed on each iteration iris = load_iris() plot_idx = 1 models = [DecisionTreeClassifier(max_depth=None), RandomForestClassifier(n_estimators=n_estimators), ExtraTreesClassifier(n_estimators=n_estimators), AdaBoostClassifier(DecisionTreeClassifier(max_depth=3), 将上面的代码加上注释

下面是对该代码的注释：

# 导入需要的库和模块
from sklearn.datasets import load_iris
from sklearn.tree import DecisionTreeClassifier
from sklearn.ensemble import RandomForestClassifier, ExtraTreesClassifier, AdaBoostClassifier
import matplotlib.pyplot as plt
import numpy as np

# 定义需要的参数
n_classes = 3   # 类别数
n_estimators = 30   # 集成模型中基分类器的数量
plot_colors = "ryb"   # 绘图时使用的颜色
cmap = plt.cm.RdYlBu   # 绘图时使用的颜色映射
plot_step = 0.02  # 决策面轮廓线的细度
plot_step_coarser = 0.5  # 粗略分类器猜测的步骤宽度
RANDOM_SEED = 13  # 每次迭代时固定种子

# 加载鸢尾花数据集
iris = load_iris()

# 设置绘图的子图位置
plot_idx = 1

# 定义四个基分类器
models = [DecisionTreeClassifier(max_depth=None),  # 决策树
          RandomForestClassifier(n_estimators=n_estimators),  # 随机森林
          ExtraTreesClassifier(n_estimators=n_estimators),  # 极端随机树
          AdaBoostClassifier(DecisionTreeClassifier(max_depth=3),  # AdaBoost
                             n_estimators=n_estimators)]

# 开始绘制四个基分类器的决策面
for pair in ([0, 1], [0, 2], [2, 3]):
    for model in models:
        # 从数据集中选取两个特征作为x轴和y轴
        X = iris.data[:, pair]
        y = iris.target

        # 随机化样本，将数据集分成训练集和测试集
        idx = np.arange(X.shape[0])
        np.random.seed(RANDOM_SEED)
        np.random.shuffle(idx)
        X = X[idx]
        y = y[idx]
        half = int(X.shape[0] / 2)
        X_train, X_test = X[:half], X[half:]
        y_train, y_test = y[:half], y[half:]

        # 训练基分类器
        model.fit(X_train, y_train)

        # 绘制训练集和测试集的散点图
        plt.subplot(3, 4, plot_idx)
        plt.tight_layout()
        plt.scatter(X_train[:, 0], X_train[:, 1], c=y_train, cmap=cmap, edgecolor='k')
        plt.scatter(X_test[:, 0], X_test[:, 1], c=y_test, cmap=cmap, alpha=0.6, edgecolor='k')

        # 绘制决策面轮廓线
        xx, yy = np.meshgrid(np.arange(X[:, 0].min() - 1, X[:, 0].max() + 1, plot_step),
                             np.arange(X[:, 1].min() - 1, X[:, 1].max() + 1, plot_step))
        Z = model.predict(np.c_[xx.ravel(), yy.ravel()])
        Z = Z.reshape(xx.shape)
        cs = plt.contourf(xx, yy, Z, cmap=cmap, alpha=.5)

        # 绘制分类器猜测的决策面轮廓线
        xx_coarser, yy_coarser = np.meshgrid(np.arange(X[:, 0].min() - 1, X[:, 0].max() + 1, plot_step_coarser),
                                             np.arange(X[:, 1].min() - 1, X[:, 1].max() + 1, plot_step_coarser))
        Z_points_coarser = model.predict(np.c_[xx_coarser.ravel(), yy_coarser.ravel()]).reshape(xx_coarser.shape)
        cs_points = plt.scatter(xx_coarser, yy_coarser, s=15, c=Z_points_coarser, cmap=cmap, edgecolor='none')

        # 设置图像的标题和绘图的标签
        plt.title(pair)
        plot_idx += 1

# 显示绘制结果
plt.suptitle("Classifiers on feature subsets of the Iris dataset")
plt.axis("tight")
plt.show()