# Artificial neural network

An **artificial neural network** (ANN) is an interconnected group of artificial neurons that uses a mathematical or computational model for information processing based on a connectionist approach to computation.

## Contents

## Structure[edit]

Neurons in artificial neural networks are generally structured in layers, each layer holding several neurons. This structure can be quite different.

Three different structures are shown here:

## Neuron[edit]

A artificial neural network is build from several Neurons. A Neuron can be drawn in the following way:

## Activation functions[edit]

Neurons can have different activation functions.

Three different functions are described here:

### Hard limit function[edit]

A neuron with a hard limit function

### Piecewise linear function[edit]

### Sigmoid function[edit]

A sigmoid function is also called a McCulloch-Pitts Model. can have a variable slope parameter

## Specific types[edit]

### Elman Networks[edit]

Elman Networks are special artificial neural networks which have a memory and thus are able to represent time in an implicit way.

### Time Delay Neural Networks[edit]

Time Delay Neural Networks (TDNNs) are special artificial neural networks which receive input over several time steps. Time is represented in an explicit way. The image shows an two-layer TDNN with neuron activations.