Trying to rate the world's literary giants is tricky at best. Do you go by the number of books sold? The long-term cultural impact? If you're Dartmouth College researcher Allen Riddell, you make computers decide. As part of an effort to determine which books would be most valuable in the public domain, Riddell has developed an author ranking algorithm that determines the most important authors who died in a given year. The system ranks writers based on the age, length and popularity of their Wikipedia articles, along with the number of titles they have in the public domain. If an author gets a lot of attention but doesn't have many freely available works, that person climbs the charts and is more likely to have titles published on free literature sites like Project Gutenberg.