Partition functions are usually hard to compute as they require a sum or integral over the entire parameter space. In this case, it's "Z is a normalizing constant, that is: it's the sum of the values of all possible assignments."

So perhaps sum_x { exp( sum_i { w[i] * g[i](x) } ) }

tel is 100% correct.

And you're right, it is a little glossed over, I'll try to be more explicit. Thanks for the comment!

Ugh! That was silly... It's fixed now, thanks!