4. introduction to neural network

Suppose we have f(x,y,z) = (x+y)z

Then graph can be represented this way:

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X         
  
   (+)--> q ---(*)--> f
  /           /
Y            /
            /
           /
Z---------/

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q = (x+y)              # dq/dx = 1 , dq/dy = 1
f = qz                 # df/dq = z , df/dz = q

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df/dq = z
df/dz = q
df/dx = df/dq * dq/dx = z * 1 = z       # Chain rule
df/dy = df/dq * dq/dy = z * 1 = z       # Chain rule

在进行反向传播的时候使用计算图会很方便

越是使用简单的操作作为节点，节点就会越多，计算图就会越大

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