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# BNNS.ActivationFunction.sigmoid

An activation function that returns the sigmoid function of its input.

```
case sigmoid
```

## Discussion

This constant defines an activation function that returns values using the logistic function:

```c
1.0 / (1.0 + exp(-x))
```

The following illustrates the output that the activation function generates from inputs in the range `-10...10`:

![Graph that shows input values for the activation function on horizontal axis and its output values on vertical axis. ](images/com.apple.accelerate/media-3654652@2x.png)

---

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