Deep Neural Networks - Deep L-layer Neural network

The notes when study the Coursera class by Mr. Andrew Ng "Neural Networks & Deep Learning", section 4.1 "Deep L-layer Neural network". It shows what deep NN looks like and notations to denote and compute NN. Share it with you and hope it helps!
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What is a deep neural network (NN)?

Figure-1

Figure-1 shows NN with different hidden layers. We can call NN with more than 1 hidden layer as deep NN (?). Logistic regression can be seen as one layer NN

Figure-2

 

Figure-2 is a 4-layer NN with 3 hidden layers.  Followings are the notations to denote and compute NN:

• L=4: the number of layers of the NN
• : the number of nodes/units in layer
  So:
  
  
  
  
  
• : the activation of layer
  and,
  
• and : the weight for computing value of
• 
• 

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