A simple metric on the space of the publishing mathematicians. That space consists of the discrete nodes that represent each publishing mathematician. For each jointly publication there is a link between the two nodes representing authors of that publication. If two authors have N common publications, the link connecting them has weight N. A distance between two nodes (x and y) is defined as the shortest number of steps from x to y. The Erdos Number is the distance (metric) of x to the one specific node (Paul Erdos). Majority of the nodes in the space belong to a one extremely large cluster/graph (a dominant/principal component). Still, there are many solitary nodes.
- The Erdos Number Project – http://www.oakland.edu/enp/