机器学习(七) — 决策树

model 4 --- decision tree

1 decision tree

1. component

usage: classification

  1. root node
  2. decision node

2. choose feature on each node

maximize purity (minimize inpurity)

3. stop splitting

  1. a node is 100% on class
  2. splitting a node will result in the tree exceeding a maximum depth
  3. improvement in purity score are below a threshold
  4. number of examples in a node is below a threshold

2 meature of impurity

use entropy( H H H) as a meature of impurity

H ( p ) = − p l o g 2 ( p ) − ( 1 − p ) l o g 2 ( 1 − p ) n o t e : 0 l o g 0 = 0 H(p) = -plog_2(p) - (1-p)log_2(1-p)\\ note: 0log0 = 0 H(p)=−plog2(p)−(1−p)log2(1−p)note:0log0=0

3 information gain

1. definition

i n f o m a t i o n _ g a i n = H ( p r o o t ) − ( w l e f t H ( p l e f t ) + w r i g h t H ( p r i g h t ) ) infomation\_gain = H(p^{root}) - (w^{left}H(p^{left}) + w^{right}H(p^{right})) infomation_gain=H(proot)−(wleftH(pleft)+wrightH(pright))

2. usage

  1. meature the reduction in entropy
  2. a signal of stopping splitting

3. continuous

find the threshold that has the most infomation gain

4 random forest

  1. generating a tree sample
复制代码
given training set of size m
for b = 1 to B:
	use sampling with replacement to create a new training set of size m
	train a decision tree on the training set
  1. randomizing the feature choice: at each node, when choosing a feature to use to split, if n features is available, pick a random subset of k < n(usually k = n k = \sqrt{n} k=n ) features and alow the algorithm to only choose from that subset of features
相关推荐
居然JuRan14 分钟前
从零开始学大模型之预训练语言模型
人工智能
martinzh35 分钟前
向量化与嵌入模型:RAG系统背后的隐形英雄
人工智能
新智元1 小时前
学哲学没出路?不好意思,现在哲学就业碾压 CS!
人工智能·openai
AI码上来1 小时前
当小智 AI 遇上数字人,我用 WebRTC 打造实时音视频应用
人工智能·webrtc·实时音视频
一只懒洋洋1 小时前
K-meas 聚类、KNN算法、决策树、随机森林
算法·决策树·聚类
黎燃1 小时前
智能库存管理的需求预测模型:从业务痛点到落地代码的完整实践
人工智能
机器之心1 小时前
DPad: 扩散大语言模型的中庸之道,杜克大学陈怡然团队免训推理加速61倍
人工智能·openai
一车小面包1 小时前
人工智能中的线性代数总结--简单篇
人工智能·numpy
大模型真好玩1 小时前
深入浅出LangGraph AI Agent智能体开发教程(四)—LangGraph全生态开发工具使用与智能体部署
人工智能·python·mcp
算家计算1 小时前
OpenAI百亿美元造芯计划曝光,算力争夺战进入新阶段?
人工智能·openai·资讯