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annotate docs/summary_of_gradient_descent.txt @ 55:0908b6cd3217

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[regression] add better cost function for sigmoids
author Jeff Hammel <k0scist@gmail.com>
date Sun, 24 Sep 2017 15:30:15 -0700
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1 # Summary of Gradient Descent
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2
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3 For a two layer network. The `[]`s denote the layer number.
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4 `'` denotes prime. `T` denotes transpose.
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5
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6 ## Scalar implementation
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7
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8 ```
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9 dz[2] = a[2] - y
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10 dW[2] = dz[2]a[1]T
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11 db[2] = dz[2]
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12 dz[1] = W[2]Tdz[2] * g[1]'(z[1])
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13 dW[1] = dz[1]xT
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14 db[1] = dz[1]
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15 ```
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16
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17
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18 ## Vectorized Implementation
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19
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20 ```
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21 dZ[2] = A[2] - Y
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22 dW[2] = (1/m)dZ[2]A[1]T
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23 db[2] = (1/m)*np.sum(dZ[2], axis=1, keepdims=True)
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24 dZ[1] = W[2]TdZ[2] * g[1]'(z[1])
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25 db[1] = (1/m)*np.sum(dZ[1], axis=1, keepdims=True)
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26 ```