Information Storage in the Weighted Sum

The weighted sum is used for a lot of things. I suppose currently it is most being used for neural networks. Maybe a billion trillion are calculated every day.
And yet the neural network books don’t go any deeper than it is a summie thingie.
Or at least I haven’t see a book recently that had any detail, perhaps a few from the 1980s went a little deeper.
Perhaps it would be nice to learn a little more about its behavior and math with Processing P5: