The price of a path: length + via penalty + bend penalty + crowding penalty. The router finds the cheapest path, so the cost function decides what "good" means.
How it looks
Drawing: a made-up example, not CORE3588
The cost function is a formula, so this is a drawing: two legal ways to join A to B. Which one the router picks depends entirely on the prices in the formula. Numbers are made up for the example.
How it works
Where it fits
Lee and A* find the cheapest path under this formula. Negotiated congestion works by raising the crowding price round after round.
In Ants' frame, the cost function is dial 3, Judging, of the three dials.