How to get explicity equation from idnlarx model?

I could get parameters values with Gnl.Nonlinearity.Parameters command, but I need to describe the mathematical equation. The model 'Gnl', in annex, was identified using sigmoidnet property. The simoidnet help express function as $F(x)=(x−r)PL + a_1*f((x−r)Qb_1+c_1) + … + a_n*f((x−r)Qb_n+c_n) + d$, where $f$ is the sigmoid function $f(z)=(1)/(e^−z+1)$. But how this expression is linked with idnlarx model equation?

How could I get the explicit mathematical equation from a idnlarx model?