sigmoid_diag_connection_impl
============================

A version of diag\_connection where inhibitory components are scaled with a 
sigmoid
function.  The `excitation` parameter is multiplies by the matches source value
and added to `inhibtion` multiplied by the sum of a sigmoid function of each of
the mismatching source values.  The sigmoid function is `m/(d+exp(s*(x-i)))`; the
parameter names are `inhibition_multiplier` for `m`; `inhibition_denom_add` for
`d`; `inhibition_slope` for `s`; and `inhibition_inflexion` for `i`.

Parameters
----------

	parameter		default_value
	inhibition		0
	excitation		0
	inhibition_multiplier	1
	inhibition_slope	1
	inhibition_inflexion	.5