Basic functionality that most of the neural layers require.

FeedforwardLayer: This class represents one layer in a feed forward neural network. This layer could be input, output, or hidden, depending on its placement inside of the FeedforwardNetwork class. An activation function can also be specified. Usually all layers in a neural network will use the same activation function. By default this class uses the sigmoid activation function.

HopfieldLayer: This class implements a Hopfield neural network. A Hopfield neural network is fully connected and consists of a single layer. Hopfield neural networks are usually used for pattern recognition.

SelfOrganizingMap: The Self Organizing Map, or Kohonen Neural Network, is a special type of neural network that is used to classify input into groups. The SOM makes use of unsupervised training.