# Apply the Sigmoid Function

Learn how to use the sigmoid function to calculate the outputs of the hidden and final layers.

## We'll cover the following

## Sigmoid function in `scipy`

Here’s the formula of the sigmoid function:

$O_\text{hidden} = \text{sigmoid}( X_\text{hidden} )$

This should be easy, especially if the sigmoid function is already defined in a Python library. It turns out that it is. The `scipy`

library has a set of special functions, and the sigmoid function is called `expit()`

. This library is imported, just like we imported the `numpy`

library:

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