Scale Factor

The scale factor is a measure of the difference in distance scales between layers. The distance scale, dx, is the distance between neurons in retinatopic units so dx in the retina is 1.

A column's nx and ny give the base number of neurons in each direction for the column.

Each layer's nxScale and nyScale gives that layer's neuron density relative to that of the column. So, if the column's nx is 32 and the layer's nxScale is 0.5, the layer will have 16 neurons in the x-direction and dx=2.

In the OpenPV code, the scale factor is usually stored as log base 2 of the relative scale factor. Thus if nxScale = 0.5 for a layer L, then L->xScale == 1, and dx == 2 (the linear density of neurons is 1/2 that of the retina). Likewise if L->xScale == -1, then dx == 1/2 (the linear density of the neurons is 2 times that of the retina).

The scale factor is an integer. If the user-supplied nxScale is not an integer power of two, xScale will be the integer nearest log2(nxScale).