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