10.3 Projections

Projections represent a layer's connectivity with another layer. They serve as a "template" for individual connections between units in the two layers, thus simplifying the specification of general patterns of connectivity. The connectivity of the projection is specified in terms of the layer this projection's layer is receiving from. Thus if you had an input layer connected to a hidden layer, then the hidden layer would have a projection with its from field set to the input layer.

In addition to the from field, projections have a ProjectionSpec which determines the connectivity patterns to use when creating the actual connections between individual units. There are a number of different forms of connectivity that can be specified with the different ProjectionSpecs, from the simple full connectivity to different forms of random, one-to-one, and "tesselated" or repeated patterns of connectivity.

The projection object itself is primarily concerned with specifying where to receive connections from, and what kinds of connection objects to create. The ProjectionSpec is responsible for determining the pattern of connectivity.