## Duality of the QuickHull Algorithm

**Duality** is the concept that two numbers **a** and **b** can be represented in two ways: as a set of points (a,b) or as a line with the equation y = 2ax - b (this equation produces parabolic duality; other equations can be used for slope or polar duality.)

Duality of points and lines produces interesting correlations. An algorithm that finds the **convex hull** of a set of ponts corresponds exactly to an algorithm that finds the **upper and lower envelopes** of an arrangement of lines.