Coursera-Machine Learning 之 Logistic Regression (逻辑回归)-0x02
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Cost Function
Training set(训练集):
m 个训练样本
如何选择拟合参数
代价函数
线性回归:
Logistic 回归:
Note:
结合函数图像比较好理解。
Simplified cost function and gradient descent
拟合参数
针对一个新的
Output
want
Repeat {
}
Advanced Optimization(高级优化)
Optimization algorithm
Gradient descent(梯度下降)
Conjugate gradient(共轭梯度法)
BFGS(变尺度法)
L-BFGS(限制变尺度法)
后三种算法优点:
不需要手动选择学习率
一般情况下比梯度下来收敛得更快
缺点:更加复杂
Example:
function [jVal, gradient] = costFunction(theta) jVal = (theta(1) - 5)^2 + (theta(2) - 5)^2; gradient = zeros(2, 1); gradient(1) = 2*(theta(1) - 5); gradient(2) = 2*(theta(2) - 5);options = optimset('GradObj', 'on', 'MaxIter', '100');initialTeta = zeros(2,1);[optTheta, functionVal, exitFlag] = fminunc(@costFunction, initialTheta, options);
Multiclass Classification: One-vs-all
One-vs-all(one-vs-rest)
给定新的输入
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