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Coursera Machine Learning : W6 Evaluating a learning Alogritm

2021-07-31

LZN

technology

coursera cs229
W6 Evaluation

Notes

Evaluation
- Training set (60%), cross-validation set (20%), and test set (20%).
- If a learning algorithm is suffering from high variance, getting more training data is likely to help.
- Small neural network is prone to underfitting
System Design
- Start from simple model
- Plot learning curves to decide if more data, features, etc. are likely to help
- Error analysis: (1) manually examine errors (2) what potential features could help to classify them.
- Skewed Classes: Positive examples# « Negative examples#
- Precission: #True positive/#Predicted positive
- Recall: #True positives/#Actural positives
- F₁ score 2PR/(P+R)
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Coursera Machine Learning : W5 Neural Network

2021-07-19

LZN

technology

coursera cs229
W5 Backward Propagation

Notes

Cost Function and Backpropagation
- total layer number: L, nodes # in layer l: s_l, k # of units in output layer
- cost function
- Backpropagation
- Random initialization: symmetry breaking
- Arch: Reasonable default: 1 hidden layer; multiple layers: same # of nodes in each layer; more layers, better performance
- backward propagation
- cyan /saian/ 青色
- magenta 品红
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Coursera Machine Learning : W4 Neural Network

2021-07-12

LZN

technology

coursera cs229
W4 Neural Network

Notes

Neural Network
- Non-linear classification: Logistic regression may take in too many polynomial features.
- Neuron: Dendrite (input wires), Axon (output wires)
- Logistic unit: x0 –> bias unit
- An artificial neuron (single) with a sigmoid activation function
- Neural Network: Input layer, Hidden layer, and Output layer.
- a^(j)_i “activation” of unit i in layer j.
- theta^(j) = matrix of weights controlling function mapping from layer j to j+1.
- If network has s_j units in layer j and s_j+1 units in layer j+1, the theta j would be of dimension s<sub>j+1</sub>*s<sub>j</sub>+1
- Important Forward propagation representation
- Be careful with the MATLAB syntax: for i = 1:10 COLON not COMMA!
- negation 否定
- parenthese 括号
- auditory cortex 听觉皮层
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Welcome to LZN's Blog!

Coursera Machine Learning : W6 Evaluating a learning Alogritm

W6 Evaluation

Notes

Evaluation

System Design

Coursera Machine Learning : W5 Neural Network

W5 Backward Propagation

Notes

Cost Function and Backpropagation

Coursera Machine Learning : W4 Neural Network

W4 Neural Network

Notes

Neural Network