# Neural Network and Deep Learning
## Logistic Regression
$$\begin{align}
正向传递\\
z &= w^Tx + b \\
a &= \sigma(z) \\
\hat{y} &= L(a) = -ylog(\hat{y}) - (1-y)log(1-\hat{y}) \ \ 其中(\hat{y} = a) \\
反向传递 \\
\frac{dL}{da}
\end{align}$$