Model representation

Cost function
有时候也会被叫做平方误差代价函数

Gradient descent algorithm 梯度下降法

learning rate后面的部分是derivative
假如阿尔法太小，梯度就会减缓。假如阿尔法太大，梯度下降可能超过最小值。

Machine learning definition
Well-posed learning problem: A computer program is said to learn from experience E with respect to some task T and some performance measure P, if its performance on T, as measured by P, improves with experience E.

Machine learning algorithms:

• supervised learning 我们教计算机做某件事
• unsupervised learning 计算机自己总结学会做某事

Others: Reinforcement learning, recommender systems.

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supervised learning
想法是在监督学习中，对于数据集中的每个样本，我们想要算法预测并得到正确答案。
分类问题 classification problem 回归问题 regression problem

unsupervised learning
把大量的数据给到computer 计算机自习学会做某事