Frank Harary - Mathematics

Mathematics

Harary's work in graph theory was diverse. Some topics of great interest to him were:

• Graph enumeration, that is, counting graphs of a specified kind. He coauthored a book on the subject (Harary and Palmer 1973). The main difficulty is that two graphs that are isomorphic should not be counted twice; thus, one has to apply Polya's theory of counting under group action. Harary was an expert in this.
• Signed graphs. Harary invented this branch of graph theory, which grew out of a problem of theoretical social psychology investigated by the psychologist Dorwin Cartwright and Harary.
• Applications of graph theory in numerous areas, especially to social science. He was co-author of John Wiley's first eBook, Graph Theory and Geography.

Among over 700 scholarly articles Harary wrote, two were co-authored with Paul Erdős, giving Harary an Erdős number of 1. He lectured extensively and kept alphabetical lists of the cities where he spoke.