# 计算代价函数
def computerCost(X,y,theta):
m = len(y)
J = 0
J = (np.transpose(X*theta-y))*(X*theta-y)/(2*m) #计算代价J
return J
# 梯度下降算法
def gradientDescent(X,y,theta,alpha,num_iters):
m = len(y)
n = len(theta)
temp = np.matrix(np.zeros((n,num_iters))) # 暂存每次迭代计算的theta，转化为矩阵形式
J_history = np.zeros((num_iters,1)) #记录每次迭代计算的代价值
for i in range(num_iters): # 遍历迭代次数
h = np.dot(X,theta) # 计算内积，matrix可以直接乘
temp[:,i] = theta - ((alpha/m)*(np.dot(np.transpose(X),h-y))) #梯度的计算
theta = temp[:,i]
J_history[i] = computerCost(X,y,theta) #调用计算代价函数
print '.',
return theta,J_history
# 归一化feature
def featureNormaliza(X):
X_norm = np.array(X) #将X转化为numpy数组对象，才可以进行矩阵的运算
#定义所需变量
mu = np.zeros((1,X.shape[1]))
sigma = np.zeros((1,X.shape[1]))
mu = np.mean(X_norm,0) # 求每一列的平均值（0指定为列，1代表行）
sigma = np.std(X_norm,0) # 求每一列的标准差
for i in range(X.shape[1]): # 遍历列
X_norm[:,i] = (X_norm[:,i]-mu[i])/sigma[i] # 归一化
return X_norm,mu,sigma
from sklearn import linear_model
from sklearn.preprocessing import StandardScaler #引入缩放的包
# 归一化操作
scaler = StandardScaler()
scaler.fit(X)
x_train = scaler.transform(X)
x_test = scaler.transform(np.array([1650,3]))
# 线性模型拟合
model = linear_model.LinearRegression()
model.fit(x_train, y)
#预测结果
result = model.predict(x_test)
# 代价函数
def costFunction(initial_theta,X,y,inital_lambda):
m = len(y)
J = 0
h = sigmoid(np.dot(X,initial_theta)) # 计算h(z)
theta1 = initial_theta.copy() # 因为正则化j=1从1开始，不包含0，所以复制一份，前theta(0)值为0
theta1[0] = 0
temp = np.dot(np.transpose(theta1),theta1)
J = (-np.dot(np.transpose(y),np.log(h))-np.dot(np.transpose(1-y),np.log(1-h))+temp*inital_lambda/2)/m # 正则化的代价方程
return J
# 计算梯度
def gradient(initial_theta,X,y,inital_lambda):
m = len(y)
grad = np.zeros((initial_theta.shape[0]))
h = sigmoid(np.dot(X,initial_theta))# 计算h(z)
theta1 = initial_theta.copy()
theta1[0] = 0
grad = np.dot(np.transpose(X),h-y)/m+inital_lambda/m*theta1 #正则化的梯度
return grad
# S型函数
def sigmoid(z):
h = np.zeros((len(z),1)) # 初始化，与z的长度一置
h = 1.0/(1.0+np.exp(-z))
return h
# 映射为多项式
def mapFeature(X1,X2):
degree = 3; # 映射的最高次方
out = np.ones((X1.shape[0],1)) # 映射后的结果数组（取代X）
'''
这里以degree=2为例，映射为1,x1,x2,x1^2,x1,x2,x2^2
'''
for i in np.arange(1,degree+1):
for j in range(i+1):
temp = X1**(i-j)*(X2**j) #矩阵直接乘相当于matlab中的点乘.*
out = np.hstack((out, temp.reshape(-1,1)))
return out
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