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sigmod公式: $$ y = \frac{1}{1+e^{-x}} $$ sigmod求导: $$ y' = \frac{\partial y}{\partial x} = \frac{0*(1+e^{-x})-{1*(1+e^{-x})}^{'}}{(1+e^{-x})^{2}} \ =\frac{e^{-x}}{(1+e^{-x})^{2}} \ = y*(1-y) $$
softmax公式: $$ a_j = \frac{e^{z_j}}{\sum _k e^{z_k}} $$ softmax求导: $$ a_j' = \frac{\partial a_j}{\partial z_i} \ $$ 这里公式是对$z_i$求导