Any eighth grader who has finished Introductory Geometry can tell you that the shortest distance between two points is a line, but any postal worker who has hauled a mailbag along a 10-kilometer route can tell you that figuring out the shortest distance between 400 or more addresses is nearly impossible. Software aimed at doing just that recently made its commercial debut, in Denmark, with the hope of shortening mail delivery times and slashing postal-service costs.

The software, developed by Paris-based company Eurobios, takes a novel approach to what is known as the "traveling-salesman problem," which has stymied mathematicians for decades. The central challenge: adding a single new address multiplies the number of possible paths by the total number of addresses, so calculating an ideal route quickly becomes untenably time-consuming. (At present, using a standard PC to compare every possible route spanning just 100 addresses would take years.) Computer scientists have developed various programs that solve the traveling-salesman problem for limited research purposes. But according to Dave Cliff, a complexity expert at Hewlett-Packard's Bristol laboratories in England, the vast scale of postal systems meant that "until recently it wasn't worth looking at computer methods, because the processing power wasn't there."