What is machine learning?
- Arthur Samuel: The field of study that gives computers the ability to learn without being explicitly programmed.
- Tom Mitchell: A computer is said to learn from experience E with respect to some class of tasks T and performance measure P, if its performance at tasks in T, as measured by P, improves with experience E. (一台计算机在一系列测试T中的表现P，因为经验E而获得提升)
Two broad classifications
- Supervised learning
- Unsupervised learning
Supervised learning
- Every example in our dataset has a correct answer. (因为我们给定了一定的历史数据或者样本数据)
Supervised learning的分类：
Regression problem (回归问题)
通过回归来预测持续的变量
Classification problem (分类问题)
通过分类来预测离散的变量
Unsupervised learning
For unsupervised learning, we may not have or have a little data sample with the label, but we still can finish approach problem by deriving the structure form data based on relationships among the variable in the data. (对于无监督学习产生的结果，我们无法对其进行反馈，因为我们没有或者只有极少的验证集)
- Clustering(聚类)
- Non-clustering(非聚类)
