“…These structures can result from some global optimization problem that has connections with graph theory. For example, Dijkstra's shortest path algorithm [1,2] can be used to find the lowest energy path of a vortex line in a disordered superconductor [3,4], and these paths are self-affine. Excitations in a disordered XY model in two dimensions [5,6], domain walls in spin glasses [7], and boundaries between drainage basins [8] are examples of physical objects with fractal dimension that are found by global optimization.…”