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1. 等高线示例
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
# 计算x,y坐标对应的高度值
def f(x, y):
return (1-x/2+x**5+y**3) * np.exp(-x**2-y**2)
# 生成x,y的数据
n = 256
x = np.linspace(-3, 3, n)
y = np.linspace(-3, 3, n)
# 把x,y数据生成mesh网格状的数据,因为等高线的显示是在网格的基础上添加上高度值
X, Y = np.meshgrid(x, y)
# 填充等高线
plt.contourf(X, Y, f(X, Y))
# 显示图表
plt.show()
2. SVM分割超平面
def plot_hyperplane(clf, X, y,
h=0.02,
draw_sv=True,
title='hyperplan'):
# create a mesh to plot in
x_min, x_max = X[:, 0].min() - 1, X[:, 0].max() + 1
y_min, y_max = X[:, 1].min() - 1, X[:, 1].max() + 1
xx, yy = np.meshgrid(np.arange(x_min, x_max, h),
np.arange(y_min, y_max, h))
plt.title(title)
plt.xlim(xx.min(), xx.max())
plt.ylim(yy.min(), yy.max())
plt.xticks(())
plt.yticks(())
Z = clf.predict(np.c_[xx.ravel(), yy.ravel()]) # SVM的分割超平面
# Put the result into a color plot
Z = Z.reshape(xx.shape)
plt.contourf(xx, yy, Z, cmap='hot', alpha=0.5)
markers = ['o', 's', '^']
colors = ['b', 'r', 'c']
labels = np.unique(y)
for label in labels:
plt.scatter(X[y==label][:, 0],
X[y==label][:, 1],
c=colors[label],
marker=markers[label])
# 画出支持向量
if draw_sv:
sv = clf.support_vectors_
plt.scatter(sv[:, 0], sv[:, 1], c='y', marker='x')
from sklearn import svm
from sklearn.datasets import make_blobs
# 生成一个有两个特征、包含两种类别的数据集
X, y = make_blobs(n_samples=100, centers=2,
random_state=0, cluster_std=0.3)
clf = svm.SVC(C=1.0, kernel='linear')
clf.fit(X, y)
plt.figure(figsize=(12, 4), dpi=144)
plot_hyperplane(clf, X, y, h=0.01,
title='Maximum Margin Hyperplan')
3. 使用不同核函数的分割超平面
首先生成一个有两个特征、包含三个类别的数据集,然后构造4个SVM算法来拟合数据集,分别是线性核函数、三阶多项式核函数、r=0.5的高斯核函数,以及r=0.1的高斯核函数。
最后把这4个SVM算法拟合出来的分割超平面画出来。
from sklearn import svm
from sklearn.datasets import make_blobs
X, y = make_blobs(n_samples=100, centers=3,
random_state=0, cluster_std=0.8)
clf_linear = svm.SVC(C=1.0, kernel='linear')
clf_poly = svm.SVC(C=1.0, kernel='poly', degree=3)
clf_rbf = svm.SVC(C=1.0, kernel='rbf', gamma=0.5)
clf_rbf2 = svm.SVC(C=1.0, kernel='rbf', gamma=0.1)
plt.figure(figsize=(10, 10), dpi=144)
clfs = [clf_linear, clf_poly, clf_rbf, clf_rbf2]
titles = ['Linear Kernel',
'Polynomial Kernel with Degree=3',
'Gaussian Kernel with $\gamma=0.5$',
'Gaussian Kernel with $\gamma=0.1$']
for clf, i in zip(clfs, range(len(clfs))):
clf.fit(X, y)
plt.subplot(2, 2, i+1)
plot_hyperplane(clf, X, y, title=titles[i])