Pretty pictures and diagrams

This is a new film which presents a slideshow on ‘Pretty Pictures and Diagrams’, or PPAD, which is actually a technical acronym for ‘Polynomial Parity Argument with Direction’. This ‘parity argument’ says that a path that starts somewhere and does not branch must end somewhere, so it has a pair of endpoints. The path represents a computation path that finds an equilibrium in an economic model. The film shows, in pictures, how such a path-following method works: A knight can find his princess in a castle if each room has only one door. An abstract scenario of ‘triangle partitions’ that are connected by following a path of ‘triangle flipping’ via ‘butterflies’ is then considered. However, these paths can be exponentially long. Hence, path-following is sometimes impractical, and we need research into other methods for finding an economic equilibrium.