Deep Black BoxOpen up the black box of AI one problem at a time, with your own hands. 21 problems in all.
Question 9

One layer, and the middle can be fenced off

This is what “one layer inserted” looks like

Get 38 or more of them right.

How each โ— bends 13 knobs
0 steps
Press [One step].
There is one function. The 40 go through it one at a time — we are not building 40 separate functions
What goes on inside a single โ— — following it line by line, from where the numbers come from
Why the bend is needed — think of it as folding paper
Why it folds — what those dotted lines above are doing
What happens as bends are added — the dashed line is the real boundary (the arc)
What to take away
A form with no layer is called a simple perceptron, a form with one layer or more a multilayer perceptron, and the bend itself an activation function.
Where this pays off
You can tell apart “the knobs are set badly” from “the shape is not enough”.
Problem 8 was the second kind. Adding one layer got us there.
Walking downhill settles at 30 correct (counting every combination in Problem 8 reached 35). Walking downhill is not raising the number of correct answers directly; it is lowering the error in the probabilities, so it can fall short of the best count.