sparse_connection_impl
======================

Operates like a matrix (for multiplication) with a large number of `inhibition`
values and a small number of `excitation` values.  Notionally, for each
dimension at the target layer, there is a small number of matching dimensions
at the source layer, from which it receives excitation rather than inhibition.

Parameters
----------

	parameter	default_value
	excitation	1
	inhibition	0

details
-------

	some_spc details

Print a human-readable list of excitation mappings; each row represents a
dimensions on the target layer representation, and lists the "matching"
dimension numbers on the source layer representation.