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，副教授 (Associate Professor)，资讯工程学系 (Computer Science and Information Engineering)

The Learning Problem

What Is Machine Learning

• observation → learning → skill
• data → ML → skill
• skill ↔ improve some performance measure
• machine learning: improve some performance measure with experience computed from data
• ML: an alternative route to build complicated system
  • some use scenarios
    

Key Essence of Machine Learning

• 具有潜在的模式
• 不能简单的编写出来程序
• 大量的数据

Examples

Applications of Machine Learning

• Food, Housing, Transport. Clothes. Education, Entertainment
• Learn our performances
• Examples
  

Components of Machine Learning

• input: $x\in \mathcal X$
• output: $y\in \mathcal Y$
• unknown pattern to be learnt (target function): $f:\mathcal X \rightarrow \mathcal Y$
• data (training examples): $\mathcal D=\{(x_1,y_1),(x_2,y_2),...,(x_N,y_N) \}$
• hypothesis (skill with hopefully good performance): $g:\mathcal X \rightarrow \mathcal Y$
• $\{(x_n,y_n) \} \ from\ f \rightarrow ML \rightarrow g$ , $f$ 是真正的模式，但学不到，$g$ 是学习之后给出的模式
• 
  • $f$ is unknown (no programmable definition)
  • 希望 $g$ 和 $f$ 尽量接近（假设函数和目标函数）
  • assume $g\in \mathcal H = \{h_k \}$, hypothesis set $\mathcal H$ can contain good or bad hypotheses
  • learning algorithm $\mathcal A$ to pick the ‘best’ one as $g$
• machine learning: use data to compute hypothesis $g$ that approximates target $f$

Machine Learning and Other Fields

Machine Learning and Data Mining

• 资料勘探即数据挖掘 (Data Mining)

  use huge data to find property that is interesting

• if ‘interesting property’ same as ‘hypothesis that approximate target’ —— ML = DM

• if ‘interesting property’ related to ‘hypothesis that approximate target’ —— DM can help ML, and vice versa (but not always)

• traditional DM also focuses on efficient computation in large database

Machine Learning and Artificial Intelligence

• 人工智能 (Artificial Intelligence)

  compute something that shows intelligent behavior

• ML is one possible route to realize AI (机器学习是实现人工智能的一种方法)

• g≈f
  $$
  g
  ≈
  f
  $g\approx f$ is something that shows intelligent behavior