Representing the Input Space
InputSpace2D.m, InputSpace3D.m, InputSpaceToOutput3D.m, and ActivationColor.m

These modules realize the functionality described in Section 3.2.1. Descriptions per module follow:

ActivationColor.m

Returns an RGB coded color according the activation value of a unit between 0 and 1. At the time of writing this document, the color selection will be, shades of red for activation levels above 0.6 and brightening towards 1, shades of blue for activation levels below 0.4 and brightening towards 0, and a pastel pink color at the range 0.4 -0.6, to give an idea of the orientation¹³ of the separation plane.

InputSpace2D.m

Is the module that opens a figure for each hidden unit in the network and draws a plot as seen in Figure 3 and described in Section 3.2.1. This module will only work for networks with two inputs as described in the same section. The following variables can be changed to customize execution:

step 

The amount with whose increments the input space will be examined. The axis variables will be incremented by this value along their respective ranges. Decreasing this value should make the graphs look more smooth, whereas increasing will make it coarse but make it drawn fast.

range 

Assuming equal ranges for all axes, the variable is an array covering the range of the input space with step  increments as described above.

The module executes by first calculating the feedforward formulas of the network and collecting the activation values of hidden units in matrices (the cell array act). Then surface graphs (see MATLAB command surf in Section 5) are drawn by using this data in separate figures.